W3C WD-object-960226

Inserting objects into HTML

W3C Working Draft 26-Feb-96

This version:
Latest version:
Dave Raggett <dsr@w3.org>
Charlie Kindel, Microsoft Corporation
Lou Montulli, Netscape Communications Corp.
Eric Sink, Spyglass Inc.
Wayne Gramlich, Sun Microsystems
Jonathan Hirschman, Pathfinder
Tim Berners-Lee, W3C
Dan Connolly, W3C

Status of this document

This is a W3C Working Draft for review by W3C members and other interested parties. It is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to use W3C Working Drafts as reference material or to cite them as other than "work in progress". A list of current W3C working drafts can be found at: http://www.w3.org/pub/WWW/TR

Note: since working drafts are subject to frequent change, you are advised to reference the above URL, rather than the URLs for working drafts themselves.


The HyperText Markup Language (HTML) is a simple markup language used to create hypertext documents that are portable from one platform to another. HTML documents are SGML documents with generic semantics that are appropriate for representing information from a wide range of applications. This specification extends HTML to support the insertion of multimedia objects including Java applets, Microsoft Component Object Model (COM) objects (e.g. OLE Controls and OLE Document embeddings), and a wide range of other media plug-ins. The approach allows objects to be specified in a general manner and provides the ability to override the default implementation of objects.

Closely related to this draft are the drafts for HTML Scripting and Forms. Readers are encouraged to treat all three documents as a single whole.

Previous Work

Previously this draft was known as the "INSERT" draft. However, on 2/13/96 the authors decided, with input from various parties, to rename the elements defined by the specification. Thus the document was renamed from WD-insert to WD-object.



HTML 2.0 defined only a single mechanism for inserting media into HTML documents: the IMG tag. While this tag has certainly proved worthwhile, the fact that it is restricted to image media severely limits it usefulness as richer and richer media finds its way onto the Web.

Developers have been experimenting with ideas for dealing with new media: Microsoft's DYNSRC attribute for video and audio, Netscape's EMBED tag for compound document embedding, and Sun's APP and APPLET tags for executable code.

Each of these proposed solutions attacks the problem from a slightly different perspective, and on the surface are each very different. In addition, each of these proposals falls short, in one way or another, of meeting the requirements of the Web community as a whole. However, we believe that this problem can be addressed with a single extension that addresses all of the current needs, and is fully extensible for the future.

This specification defines a new tag <OBJECT> which subsumes the role of the IMG tag, and provides a general solution for dealing with new media, while providing for effective backwards compatibility with existing browsers. OBJECT allows the HTML author to specify the data, including persistent data and/or properties/parameters for initializing objects to be inserted into HTML documents, as well as the code that can be used to display/manipulate that data. Here, the term object is used to describe the things that people want to place in HTML documents, but other terms for these things are: components, applets, plug-ins, media handlers, etc.

The data can be specified in one of several ways: a file specified by a URL, in-line data, or as a set of named properties. In addition, there are a number of attributes that allow authors to specify standard properties such as width, and height. The code for the object is specified in several ways: indirectly by the object's "class name", by information included as part of the object's data, and the combination of an object class name and a network address.

This specification covers the syntax and semantics for inserting such objects into HTML documents, but leaves out the architectural and application programming interface issues for how objects communicate with the document and other objects on the same page. It is anticipated that future specifications will cover these topics, including scripting languages and interfaces.

An introduction to the OBJECT tag

This section is intended to help readers get the feel of the insertion mechanism, and is not a normative part of the specification. The OBJECT tag provides a richer alternative to the IMG tag. It may be used when the author wishes to provide an alternative for user agents that don't support a particular media. A simple example of using OBJECT is:

    <OBJECT data=TheEarth.avi
    <img src=TheEarth.gif alt="The Earth">

Here the user agent would show an animation if it supports the AVI format, otherwise it would show a GIF image. The IMG element is used for the latter as it provides for backwards compatibility with existing browsers. The TYPE attribute allows the user agent to quickly detect that it doesn't support a particular format, and hence avoid wasting time downloading the object. Another motivation for using the TYPE attribute is when the object is loaded off a CD-ROM, as it allows the format to be specified directly rather than being inferred from the file extension.

The next example inserts an OLE control for a clock:


The ID attribute allows other controls on the same page to locate the clock. The DATA attribute points to the persistent stream data used to initialize the object's state. It includes a class identifier. The CODE attribute points to a file containing the implementation for this object. The file may contain the code for several classes, but this can be resolved by the class id from the object's data stream.

In the absence of the CODE attribute, the class identifier may be sufficient to locate the code implementing this object. User agents may provide a range of mechanisms for locating and downloading such code. For some formats such as image files, the Internet media type returned with the data is sufficient.

The class identifier can be specified explicitly using the CLASSID attribute. This value takes precedence over a class identifier included as part of the object's data, e.g.


In this example, CLASSID is specified via Component Object Model "class id" URL scheme. A "clsid" is a universally unique identifier (uuid) as defined by OSF/DCE RPC. Other object systems, such as Java, have their own URL schemes ("java:").

For speedy loading of objects you can inline the object's state data using the new URL scheme "data:", e.g.

       type="application/x-oleobject; clsid=no"

The data is expressed as a Base64 encoded byte stream. The interpretation of this stream is class dependent. If the CLASSID attribute is missing or is insufficient to disambiguate the precise format of this stream then the TYPE attribute may be used to resolve matters. In the example, the Internet media type for COM streams takes a parameter that indicates that the stream doesn't start with a class identifier.

The next example is a Java applet:

    <OBJECT code="BounceItem.class" width=500 height=300>

This is the bouncing heads demo. The implementation is specified by a relative URL and dereferenced with respect to the document URL. The images for the heads are loaded by the Java program as follows:

    bounceimages[i-1] = getImage(getCodeBase(), "images/jon/T" + i + ".gif");

The getCodebase() function returns the URL used to retrieve the Java program, and is used here to dereference the relative URL (e.g. "images/jon/T1.gif") used for each image.

The semantics of the CLASSID attribute and the Java name space are still under discussion. The following is therefore liable to change. The previous example could have used the CLASSID attribute to specify the class name, e.g. CLASSID="java:BounceItem.class". The user agent would then use the Java specific mechanism to locate the code for this class, in this case, to first check if BounceItem.class is already installed, and if not to treat it as a relative URL, which is dereferenced with respect to the URL supplied by the CODE attribute if present, otherwise with respect to the document URL, e.g.

    <param name=text value="This is the Applet Viewer">

In the absence of the CLASSID, user agents may obtain the Java class name from information supplied with the code itself or from the URL used to retrieve the code. The other attributes on the OBJECT element define rendering properties of the container for the applet viewer. The PARAM element specifies a named property which is used to initialize the class.

Because the OBJECT tag enables arbitrary code ("applets", if you will) to be downloaded an executed. The DATA attribute and the PARAM tags allow the HTML author to specify the data to be used by the applet. One application of this is in the area of HTML scripting, whereby the "applet" specified by the OBJECT tag is actually a script interpreter engine. This feature enables arbitrary programming languages to be used from within HTML. For example if there were an implementation of the Perl language interpreter as a COM object, the following could appear in the HTML documents HEAD section:

          <![ %if-script [
                 # perl script here

The <![ and ]]> in this example indicates an SGML marked section, which hides the script code from downlevel browsers. See the W3C working draft on HTML3 Scripting for more information on the SCRIPT tag.

A walk through the DTD

The document type definition provides the formal definition of the allowed syntax for HTML inserts. The following is an annotated listing of the DTD defining the semantics of the elements and their attributes. The complete listing appears at the end of this document.

Standard Units for Lengths

Length values can be specified as an integer representing the number of screen pixels, or as a percentage of the current displayable region, for widths, this is the space between the current left and right margins, while for heights, this is the height of the current window or table cell etc.

Additional units may be added in the future to give designers greater control over the size of objects relative to fonts specified in fixed units such as points, picas, inches and centimeters.

Note: Shouldn't we add these now for consistency with HTML3 tables? The additional implementation effort would be minimal - with pt for points, pi for picas, in for inches, and cm for centimeters, where 72pt = 6pi = 1in = 2.54cm.

An opposing position is to use a style sheet language to specify the width and height, e.g. with the STYLE attribute or indirectly via the ID attribute. Perhaps the WIDTH and HEIGHT attributes should be considered as forming part of the style sheet? In which case, it would make sense to add the desired units (CSS uses the same notation as proposed above).


The OBJECT element is used to insert an object into an HTML document. It requires both start and end tags. The OBJECT element has the same content model as the HTML BODY element, except that one or more optional PARAM, or EVENT elements can be placed immediately after the OBJECT start tag and used to initialize the inserted object. The content of the OBJECT element is rendered if the object specified by the data, code or classid attributes can't be rendered (user agents may choose to display the content of the OBJECT element if displaying the actual element will take a long time to render). This provides for backwards compatibility with existing browsers, and allows authors to specify alternative media via nested OBJECT elements.

Note that this doesn't provide the same level of flexibility as would be provided by a richer description of resource variants. For instance when a resource in available are several media types and for each such type in English, Spanish, French and German.

<!-- Content model entities imported from parent DTD:
  %body.content allows inserts to contain headers, paras,
  lists, form elements and even arbitrarily nested inserts.
<!ENTITY % attrs
       "id      ID       #IMPLIED  -- element identifier --
        class   NAMES    #IMPLIED  -- for subclassing elements --
        style   CDATA    #IMPLIED  -- rendering annotation --
        dir   (ltr|rtl)  #IMPLIED  -- I18N text direction --
        lang    NAME     #IMPLIED  -- as per RFC 1766 --">
<!ENTITY % URL "CDATA" -- universal resource locator -->
<!ENTITY % Align "(top|middle|textmiddle|bottom|left|center|right)">
<!ENTITY % Length "CDATA" -- standard length value -->
<!-- OBJECT is a character-like element for inserting objects -->
<!ELEMENT object - - (param*, alias*, bodytext)>
<!ATTLIST object
        %attrs      -- id, class, style, lang, dir --
        declare CDATA    #IMPLIED   -- declare but do not instantiate object --
        classid %URL     #IMPLIED   -- object's UUID --
        code    %URL     #IMPLIED   -- ref to object's code --
        data    %URL     #IMPLIED   -- ref to object's data --
        type    CDATA    #IMPLIED   -- Internet media type --
        align   %Align   #IMPLIED   -- positioning inside document --
        height  %Length  #IMPLIED   -- suggested height --
        width   %Length  #IMPLIED   -- suggested width --
        border  %Length  #IMPLIED   -- suggested link border width --
        hspace  %Length  #IMPLIED   -- suggested horizontal gutter --
        vspace  %Length  #IMPLIED   -- suggested vertical gutter --
        usemap  %URL     #IMPLIED   -- ref to image map --
        ismap   (ismap)  #IMPLIED   -- use server image map -
        name    %URL     #IMPLIED   -- same as INPUT, indicates part of a submit -
<!-- the BODYTEXT element is needed to avoid problems with
      SGML mixed content, but is never used in actual documents -->
<!ELEMENT bodytext O O %body.content>

In general, all attribute names and values in this specification are case insensitive, except where noted otherwise. OBJECT has the following attributes:

Used to define a document-wide identifier. This can be used for naming positions within documents as the destination of a hypertext link. It may also be used by style sheets for rendering an element in a unique style. An ID attribute value is an SGML NAME token. NAME tokens are formed by an initial letter followed by letters, digits, "-" and "." characters. The letters are restricted to A-Z and a-z. It may also be used by the user agent or other objects in the document to find and communicate with objects on the document.
A space separated list of SGML NAME tokens. CLASS names specify that the element belongs to the corresponding named classes. These may be used by style sheets to provide class dependent renderings.
A LANG attribute identifies the natural language used by the content of the associated element.The syntax and registry of language values are defined by RFC 1766. In summary the language is given as a primary tag followed by zero or more subtags, separated by "-". White space is not allowed and all tags are case insensitive. The name space of tags is administered by IANA. The two letter primary tag is an ISO 639 language abbreviation, while the initial subtag is a two letter ISO 3166 country code. Example values for LANG include:
      en, en-US, en-uk, i-cherokee, x-pig-latin.
Human writing systems are grouped into scripts, which determine amongst other things, the direction the characters are written. Elements of the Latin script are nominally left to right, while those of the Arabic script are nominally right to left. These characters have what is called strong directionality. Other characters can be directionally neutral (spaces) or weak (punctuation).
The DIR attribute specifies an encapsulation boundary which governs the interpretation of neutral and weakly directional characters. It does not override the directionality of strongly directional characters. The DIR attribute value is one of LTR for left to right, or RTL for right to left, e.g. DIR=RTL.
The STYLE attribute allows you to include rendering information. W3C has produced a separate specifcation on how to associate HTML documents with rendering information in different notations, see W3C-style.
Used to indicate that the object is not to be instantiated, only declared. A detailed description of the DECLARE attribute is given below.
This can be used to specify a class identifier for an object. This could be a DCE universally unique object identifier (uuid), Java class name, or another type of class name as appropriate to the object system, e.g. Corba. This allows effective use of caching, as the user agent can use simple string comparison to check whether two objects are the same independent of their location.
The CLASSID attribute value takes the form of a URL scheme prefix separated by a colon from the character string defining the class identifier. The prefix is used to identify the object system for the class identifier, for example classid="clsid:{663C8FEF-1EF9-11CF-A3DB-080036F12502}" gives the (clsid) uuid for a Microsoft COM object, using the CLSID name space, while classid="java:Animator.class" gives the class name for Java applet.
CLASSID may be sufficient for the user agent to locate the code implementing the object. However, the CODE attribute can be used with CLASSID to provide a hint as to where to look for this code. The search mechanism will in general depend on the object system the identifier belongs to. Note that the value specified with CLASSID takes precedence over a class identifier derived from the object's data stream.
When searching for the implementation of an object, the CLASSID attribute takes precedence over the DATA/TYPE attributes. A decision tree giving further details on this resolution procedure appears later on in this specification. In the absence of CLASSID a value for the class identifier may be derivable from the DATA attributes, for instance the Internet media type for the DATA may sufficient, e.g. when the data is for a GIF encoded image.
This specifies a URL referencing where to find the code which implements the object's behaviour. If this URL is insufficient to locate the intended object, when for instance, a file contains the implementations for several classes, the CLASSID may be used to supply a disambiguating class identifier.
Specifies a URL referencing the object's data. This could be a GIF file or the pickled data representing an object's state. In many cases the media type or the data itself contains sufficient information to identify what code is needed to initialize the object. Note that an object's data can even be included inline for super efficient loading. This specification proposes a new URL scheme "data:". The rest of the URL is a base64 encoded character string that specifies the object's data as an opaque byte stream.
On its own, this would be meaningless. If the DATA attribute appears without a CODE or CLASSID attribute, then a TYPE attribute may be sufficient to interpret the data. For instance a Microsoft COM object can be asked to write its state using the WriteClassStream procedure. This inserts the object's class id as the first 16 bytes of the stream. If the TYPE attribute indicates that the data is in the COM persistent stream format, then the class id can be retrieved from the DATA attribute and used to find the code implementing the object's behaviour.
The CLASSID attribute can be used to override the default implementation as implied by the DATA attribute. For example, you may have the pickled data for an Excel spread sheet but want to view it with the "SuperGraph" package. You would then use the DATA attribute to point to the Excel spreadsheet data, and the CLASSID or CODE attribute to point to the SuperGraph plug-in.
The CLASSID, CODE and DATA attributes specify URLs. Any fragment identifier included as part of these URLs should be passed to the object, either directly, or by callback.
This specifies an Internet Media Type (see RFC 1590) for the object's data. The attribute can be used to allow user agents to quickly skip media they don't support, and instead to render the contents of the OBJECT element. It is also useful when loading objects off local drives as it allows the media type to be specified explicitly rather than being derived from the file extension.
The following grammar for media types is a superset of that for MIME because it does not restrict itself to the official IANA and x-token types.
       media-type     = type "/" subtype *(";" parameter )
       type           = token
       subtype        = token
where token is defined by:
       token          =  1*<any (ASCII) CHAR except SPACE, CTLs, or tspecials>
       tspecials      = <one of the set>   ( ) < > @ , ; : \ " / [ ] ? =
Parameters may follow the type/subtype in the form of attribute/value pairs.
       parameter      = attribute "=" value
       attribute      = token
       value          = token | quoted-string
The type, subtype, and parameter attribute names are case-insensitive. Parameter values may or may not be case-sensitive, depending on the semantics of the parameter name. White space characters must not be included between the type and subtype, nor between an attribute and its value.
If a given media-type value has been registered by the IANA, any use of that value must be indicative of the registered data format. Although HTML allows the use of non-registered media types, such usage must not conflict with the IANA registry. Data providers are strongly encouraged to register their media types with IANA via the procedures outlined in RFC 1590.
All media-type's registered by IANA must be preferred over extension tokens. However, HTML does not limit applications to the use of officially registered media types, nor does it encourage the use of an "x-" prefix for unofficial types outside of explicitly short experimental use between consenting applications.
This determines where to place the object. The ALIGN attribute allows objects to be placed as part of the current text line, or as a distinct unit, aligned to the left, center or right.
The following values are chosen for their ease of implementation, and their independence of other graphics occurring earlier on the same line:
For ALIGN=TEXTTOP, the top of the object is vertically aligned with the top of the current font.
For ALIGN=MIDDLE, the middle of the object is vertically aligned with the baseline.
For ALIGN=TEXTMIDDLE, the middle of the object is vertically aligned with the position midway between the baseline and the x-height for the current font. The x-height is defined as the top of a lower case x in western writing systems. If the text font is an all-caps style then use the height of a capital X. For other writing systems, align the middle of the object with the middle of the text.
For ALIGN=BASELINE, the bottom of the object is vertically aligned with the baseline of the text line in which the object appears.
For ALIGN=TEXTBOTTOM, the bottom of the object is vertically aligned with the bottom of the current font.
Note the proposed Netscape extensions for the align attribute of the IMG element are context sensitive, as are some of the implementions of ALIGN=TOP. See the test page at:
The following alignment values allow the object to float rather than being treated as part of the current line:
For ALIGN=LEFT, the object is floated down and over to the current left margin. Subsequent text is flowed past the right hand side of the visible area of the object.
For ALIGN=CENTER, the object is floated to after the end of the current line and centered between the left and right margins. Subsequent text starts at the beginning of the next line.
For ALIGN=RIGHT, the object is floated down and over to the current right margin. Subsequent text is flowed past the left hand side of the visible area of the object.
This gives the suggested width of a box enclosing the visible area of the object. The width is specified in standard units. User agents may use this value to scale an object to match the requested width if appropriate.
Smooth scaling a small image to a larger size provides an effective solution to reducing the time needed to download an image, offering better subjective results when compared to color reduction.
This gives the suggested height of a box enclosing the visible area of the object. The height is specified in standard units. User agents may use this value to scale an object to match the requested height if appropriate.
This attribute applies to the border shown when the object forms part of a hypertext link, as specified by an enclosing anchor element. The attribute specifies the suggested width of this border around the visible area of the object. The width is specified in standard units. For BORDER=0 no border should be shown. This is normally used when such a border would interfere with the visual affordances presented by the object itself. For instance, the object could render itself as a number of beveled buttons.
The suggested width of the space to the left and right of the box enclosing the visible area of the object. The width is specified in standard units. This attribute is used to alter the separation of preceding and following text from the object.
The suggested height of the space to the top and bottom of the box enclosing the visible area of the object. The height is specified in standard units.
This specifies a universal resource identifier for a client-side image map in the format proposed by Spyglass Inc. This is normally appropriate only for static images.
When the OBJECT element appears within a hypertext link, this attribute indicates that the server provides an image map, so that mouse clicks should be sent to the server in the same manner as for the IMG element. This is normally appropriate only for static images.
This provides a way for user agents which support FORMs to determine whether an INSERTed object within a FORM block should participate in the "submit" process. If NAME is specified the user agent should submit the VALUE property of the object to the host. If NAME is not specified the object is assumed to be "user interface glitter". Thus NAME is equivalent to the like named attribute of the INPUT tag.
Keyboard accelerator.
Tab order index.

More Information About OBJECT DECLARE

The DECLARE attribute of the OBJECT element is used to specify an object without inserting it into the document. Normally, OBJECT implies that the "body" requires a reference to the object. The DECLARE attribute allows HMTL authors to specify that the "body" does not directly reference the object; some other element does (via a URL that targets the OBJECT's ID value).

OBJECT markup with the DECLARE attribute imply objects that are not created (instantiated) until needed by something that references them (i.e. late binding). Each such "binding" results in a separate copy of the object. In other words, the OBJECT DECLARE is treated as a declaration for making an instance of an object.

If the declared object isn't supported, or fails to load, the user agent should try the contents of the OBJECT DECLARE element, which is currently restricted to another OBJECT DECLARE element. The TYPE attribute can be used to specify the Internet Media Type for the object as a hint for this situation.

Examples of OBJECT DECLARE Usage

The PARAM element

The PARAM element allows a list of named property values (used to initialize a OLE control, plug-in module or Java applet) to be represented as a sequence of PARAM elements. Note that PARAM is an empty element and should appear without an endtag.

<!ELEMENT param - O EMPTY -- named property value -->
<!ATTLIST param
        name    CDATA    #REQUIRED  -- property name --
        value   CDATA    #IMPLIED   -- property value --
        valueref  %URL   #IMPLIED   -- ref to object ALIAS --
        type    CDATA    #IMPLIED   -- Internet media type --

The NAME attribute defines the property name. The case sensitivity of the name is dependent on the code implementing the object.

The VALUE attribute is used to specify the property value. It is an opaque character string whose meaning is determined by the object based on the property name. Note that CDATA attribute values need characters such as & to be escaped using the standard SGML character entities, e.g. &amp; for "&". It is also essential to escape the > character to defend against incorrect handling by many existing browsers (use &gt;).

The VALUEREF attribute is used when the property is itself an object. A distinct attribute is needed as in some cases the property type cannot be deduced from the property name. VALUEREF typically provides a URL based reference to an OBJECT DECLARE element (see below) that defines the object itself.

VALUEREF can also be used to specify an object directly. For example valueref=foo.gif. Another possibility is to use inline data with the "data:" URL scheme. Both of these options save having to include an associated ALIAS element.

The TYPE attribute is required when the "data:" URL scheme is used. It specifies the media type for the data stream and allows the user agent to decode the stream, e.g. to pick out an embedded class identifier.

Using OBJECT DECLARE For Object Valued Properties In PARAM

The VALUEREF attribute of PARAM allows properties to be "object valued"; the property is an object itself. For example, Windows provides a standard Font object that is exposed as a COM object. Any OLE Control can use the "font object type" as the type of the "Font" property. The following Visual Basic example illustrates how a programmer would manipulate such a property:

Set x = CreateObject("Button")
x.Text = "Press me"
x.BackColor = vbWhite
x.Font.Face = "Courier New"
x.Font.Bold = True
x.Font.Size = 12

The equivalent OBJECT tag would look like this:

<object id="x" classid=#CLSID-CoolButton> 
   <object declare id=Btn1Font classid=#CLSID-StdFont>
      <param name="Face" value="Courier New">
      <param name="Bold" value="True">
      <param name="Size" value=12>
   <param name="Text" value="Press me">
   <param name="BackColor" value=0xFFFFFF >
   <param name="Font" valueref=Btn1Font>

Short cuts for CLASSID values

The LINK element is suitable providing "#define" like capabilities.

<link id=CLSID-CoolButton  href="clsid:{F6E6DDD0-0000-11cf-A50D-080036F12501}">
<link id=CLSID-CoolText    href="clsid:{F6E6DDD1-0000-11cf-A50D-080036F12501}">
<link id=CLSID-CoolListBox href="clsid:{F6E6DDD2-0000-11cf-A50D-080036F12501}">
<link id=CLSID-CoolCombo   href="clsid:{F6E6DDD3-0000-11cf-A50D-080036F12501}">
<link id=CLSID-CoolCheck   href="clsid:{F6E6DDD4-0000-11cf-A50D-080036F12501}">
<link id=CLSID-CoolRadio   href="clsid:{F6E6DDD5-0000-11cf-A50D-080036F12501}">

The HTML author would then cut-and paste this snippet into his HTML document near the top. He could then have OBJECT tags that looked like this:

<OBJECT id="x" classid=#CLSID-CoolButton> 
   <param name="Text" value="Press me">

Or, the list of LINK's could be placed into a separate file (say, for example cool.cid) and referenced as in the example below:

<OBJECT id="x" classid=cool.cid#CLSID-CoolButton> 
   <param name="Text" value="Press me">

Further Work

This section describes proposals for extending the capabilities of the insertion mechanism as an encouragement and guide to developers wishing to experiment with such features. These ideas are not part of the current specification, and support is not required for conformance with this specification.

Document Background

Using a GIF image to tile the document background often results in significant delays while the image tile is downloaded. The ability to use a small Java applet or OLE Control to generate the image tile would allow rich background textures and patterns to be used without causing significant delay. As processing speeds increase, using an object to generate the background would make it practical to create animated backgrounds.

The proposed extension is to allow the BACKGROUND attribute of the BODY element to reference OBJECT DECLARE elements, for example:

<title>Demo Document</title>
<object declare id=marble
<body background="#marble">
<p>This document has a marble texture generated by an applet.


Overlays are useful for reducing network bandwidth needs. For instance, you can place a PNG overlay on top of a JPEG image. If the PNG image is used for an antialiased text overlay while the JPEG image is used for an underlying photographic image with a high compression factor, then the two images will take significantly less time to send than a single image combining both layers. Selecting the format and compression for each layer separately allows you to get higher compression for the same level of quality.

Overlays also save time by making caching more effective. For instance you might send a large image on one page, and then make small changes to it on subsequent pages. Using an overlay allows the original large image to be reused, so that only the small changes need to be sent with each successive page.

<!ELEMENT overlay - O EMPTY -- image overlay -->
<!ATTLIST overlay
        id          ID          #IMPLIED  -- for naming this overlay --
        class       NAMES       #IMPLIED  -- for subclassing element --
        style       CDATA       #IMPLIED  -- for attaching style info --
        x           %Length     #IMPLIED  -- offset from left of parent --
        y           %Length     #IMPLIED  -- offset from top of parent --
        width       %Length     #IMPLIED  -- suggested width --
        height      %Length     #IMPLIED  -- suggested height --
        src         %URL        #IMPLIED  -- network address of object --

For instance, here is a road map overlayed on an aerial photograph:

    <OBJECT data="photo.jpeg">
        <overlay src=grid.png>

The SRC attribute of the OVERLAY element could be used together with an OBJECT DECLARE element. This allows you to create overlays from OLE controls or Java applets.

Non-Rectangular and Resizable Objects

Many objects will size themselves according to their contents. Another popular feature is likely to be the ability for users to dynamically resize objects, e.g. by dragging size bars. The height and width attributes of the OBJECT element can be used as suggested initial values. For instance, images can be automatically resized to match these values. The ability to smoothly magnify an image allows a small image file to fill a large space, and saves network time.

Simple user agents may consider objects as having a rectangular outline. Of course, the object can render itself with a transparent background to give the effect of a shaped object, but any text flowing past would still follow the rectangular frame around the object. Smarter user agents can "ask" the object for its outline and flow text around that.

To speed up display of the rest of the document, it is desirable to get the outline as early as possible. For this reason it makes sense to be able to specify the outine via an attribute (e.g. SHAPE) on the OBJECT element. It is suggested that the user agent scale the object to the WIDTH and HEIGHT attribute values (if given) and then to clip it to the outline as given by the SHAPE attribute. Subsequent text would then flow around the outline. The ability to offset the object relative to the outline would also be very useful. The syntax for SHAPE is left to a future specification.

Figure Captions

A time proven idiom for document layout is the figure. This is often an illustration, but may contain textual material separate from the main flow of the document. Figures are typically captioned and floated to between columns or to the top or bottom of a page. It is not uncommon to see separate contents lists for figures and tables, in addition to the main table of contents.

It is proposed that the FIG element is used to create captioned figures:

    <!ENTITY % f.align "(left|center|right)">
    <!ELEMENT fig - - (caption?, bodytext)>
    <!ATTLIST fig
        %attrs                      -- id, class, style, lang, dir --
        align   %f.align #IMPLIED   -- position on page --
        height  %Length  #IMPLIED   -- suggested height --
        width   %Length  #IMPLIED   -- suggested width --
    <!ENTITY % c.align "(top|bottom|left|right)">
    <!ELEMENT caption - - %body.content>
    <!ATTLIST caption
        %attrs                      -- id, class, style, lang, dir --
        align   %c.align #IMPLIED   -- position relative to figure --

For example:

        <caption>Mount Washington</caption>
        <OBJECT data=http://www.acme.com/images/vista.jpeg>
        <p>A spectacular view of Mount Washington during a winter sunset.

Note that FIG is a block-like element similar to tables. If a user agent supports tables then adding support for figures is quite simple, since the FIG element behaves in the same as a table with a caption and a single cell. Of course some would argue that in this case, why not use the TABLE element. This is an example of approaching HTML with a view to getting a desired visual effect without regard to what the markup means. This makes it hard to export HTML to other document formats, and makes it harder to read the markup, as you now have to guess what the author actually was trying to do.

Credits and Copyright

Image such as GIF and PNG formats allow textual messages to be included with the image data. This provides an appropriate place to store copyright messages since these will then be automatically transferred with the image when it is dragged from the document to the desktop etc. For other formats, copyright notices can be included in HTTP headers, or by wrapping up the objects as MIME multipart files.

Even when information can be included as part of the object's data, it is still useful to present a credit or copyright message to the user as part of the document text. Something immediately visible is more effective that something hidden! The suggested way of handling credits is to use a new character emphasis element CREDIT that can be given as part of the FIG contents, e.g.

        <OBJECT data=http://www.acme.com/images/vista.jpeg>
        <p>A spectacular view of Mount Washington during a winter
        <credit>John Smith</credit>

HTML Inserts DTD

The DTD or document type definition provides the formal definition of the allowed syntax for HTML inserts.

<!-- Content model entities imported from parent DTD:
  %body.content allows inserts to contain headers, paras,
  lists, form elements and even arbitrarily nested inserts.
<!ENTITY % attrs
       "id      ID       #IMPLIED  -- element identifier --
        class   NAMES    #IMPLIED  -- for subclassing elements --
        style   CDATA    #IMPLIED  -- rendering annotation --
        dir   (ltr|rtl)  #IMPLIED  -- I18N text direction --
        lang    NAME     #IMPLIED  -- as per RFC 1766 --">
<!ENTITY % URL "CDATA" -- universal resource locator -->
<!ENTITY % Align "(top|middle|bottom|left|center|right)">
<!ENTITY % Length "CDATA" -- standard length value -->
<!-- OBJECT is a character-like element for inserting objects -->
<!ELEMENT OBJECT - - (param*, event*, alias*, bodytext)>
        %attrs      -- id, class, style, lang, dir --
        data    %URL     #IMPLIED   -- ref to object's data --
        code    %URL     #IMPLIED   -- ref to object's code --
        classid %URL     #IMPLIED   -- object's UUID --
        type    CDATA    #IMPLIED   -- Internet media type --
        align   %Align   #IMPLIED   -- positioning inside document --
        height  %Length  #IMPLIED   -- suggested height --
        width   %Length  #IMPLIED   -- suggested width --
        border  %Length  #IMPLIED   -- suggested link border width --
        hspace  %Length  #IMPLIED   -- suggested horizontal gutter --
        vspace  %Length  #IMPLIED   -- suggested vertical gutter --
        usemap  %URL     #IMPLIED   -- ref to image map --
        ismap   (ismap)  #IMPLIED   -- use server image map --
        name    %URL     #IMPLIED   -- same as INPUT, indicates part of a submit --
<!-- the BODYTEXT element is needed to avoid problems with
      SGML mixed content, but is never used in actual documents -->
<!ELEMENT bodytext O O %body.content>
<!ELEMENT param - O EMPTY -- named property value -->
<!ATTLIST param
        name    CDATA    #REQUIRED  -- property name --
        value   CDATA    #IMPLIED   -- property value --
        valueref  %URL   #IMPLIED   -- ref to OBJECT DECLARE --
        type    CDATA    #IMPLIED   -- Internet media type --

Decision Tree for Binding Objects

This section defines the steps needed to bind an object given various combinations of attributes. Without a precise semantics for this, different user agents would otherwise produce different results to the frustration of authors. The basic idea is that when finding the implementation for an object the CLASSID takes precedence over CODE.

properties = GetParams();     // collect properties from PARAM elements, if any
type = AttributeValue(TYPE);  // get value of TYPE attribute 
// First try to determine the clsid
if (!(clsid = AttributeValue(CLASSID))) then
    // no CLASSID, use mime to clsid mapping
    if (clsid = TypeToCLASSID(TYPE))
       Fail("Can't load data");
fi// We now have the name of the class code (clsid),
// attempt to instantiate
if (!(class = LoadImplementation(clsid))) then
   // class code is not installed. Download it
   if (code = AttributeValue(CODE)) then
       if (!DownloadAndInstallCode(code)) then
          Fail("Can't download code");
       if (code = WellKnownSearchpath(clsid)) then
          if (!DownloadAndInstallCode(code)) then
             Fail("Can't download code");
          Fail("Can't find code");
   // Try to instantiate again
   if (!(class = LoadImplementation(clsid))) then
      Fail("Can't start code");
fi// Code is now running. Initialize with data
if (data = AttributeValue(DATA)) then
   Invoke(class, type, data, null);
else // no data, use params
   Invoke(class, null, null, params);


Cascading Style Sheets
W3C's working draft specification can be found at: "http://www.w3.org/pub/WWW/Style/css/draft.html"
HTML and Style Sheets
W3C's working draft specification on associating rendering information with HTML documents can be found at: http://www.w3.org/pub/WWW/TR
Internet Media Types - RFC 1590
J. Postel. "Media Type Registration Procedure." RFC 1590, USC/ISI, March 1994. This can be found at ftp://ds.internic.net/rfc/rfc1590.txt.
MIME - RFC 1521
Borenstein N., and N. Freed, "MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1521, Bellcore, Innosoft, September 1993. This can be found at ftp://ds.internic.net/rfc/rfc1521.txt.
Further information about the OSF Distributed Computing Environment can be found at http://www.osf.org/dce.
The Component Object Model Specification
This is available from http://www.microsoft.com/intdev/inttech/comintro.htm.
The Microsoft Internet Technologies
Complete specifications for the Microsoft internet technologies can be found at: http://www.microsoft.com/intdev/default.htm.
Client-Side Image maps
"A Proposed Extension to HTML : Client-Side Image Maps", James L. Seidman, 03 Aug 1995. draft-ietf-html-clientsideimagemap-01.txt
The markup language known as "HTML/2.0" provides for image maps. Image maps are document elements which allow clicking on different areas of an image to reference different network resources, as specified by Uniform Resource Locators (URIs). The image map capability in HTML/2.0 is limited in several ways, such as the restriction that it only works with documents served via the "HTTP" protocol, and the lack of a viable fallback for users of text-only browsers. This document specifies an extension to the HTML language, referred to as "Client-Side Image Maps," which resolves these limitations.
SGML Marked Sections
Dan Connelly has a paper on the use of SGML Marked Sections at http://www.w3.org/pub/WWW/MarkUp/WD-doctypes. And the TEI also has information: http://www.ebt.com/usrbooks/teip3/2404.
HTML3 Scripting
W3C's working draft specification on scripting in HTML documents can be found at:
HTML3 Forms
There is no forms draft...yet.

W3C: The World Wide Web Consortium: http://www.w3.org/pub/WWW/Consortium/