Appendix M: Change History

Changes with the 29 June 2000 SVG Draft Specification

• Global/miscellaneous changes
  • Replaced the two-grammar approach from the March 3 spec (i.e., Stylable SVG and Exchange SVG) with a single grammar approach which allows styling either using CSS or via corresponding XML attributes. The chapter on Exchange SVG has been removed as a result of this. See the remainder of this change history for what other changes occurred.
  • Various minor error corrections to the sections of the specification describing the language and the SVG DOM, along with various miscellaneous editorial fixes.
  • DOM: Significant changes due to consolidating Stylable SVG and Exchange SVG into a single grammar. All #ifdef STYLABLESVG and #ifdef EXCHANGESVG logic has been removed. The various DOM attributes corresponding to the XML presentation attributes have been removed in favor of a single method, getPresentationAttribute(attr-name), that is present on interface "Stylable".
  • DOM: Cleanup of SVG DOM to ensure that script writers have access to every attribute which is animatable and to make the SVG DOM use a consistent approach to presenting the current animated value, with many changes as a result. Defined new DOM interfaces such as SVGAnimatedAngle, SVGAnimatedNumber, SVGAnimatedLength, etc. and modified many attributes from previous types (e.g., SVGAngle, SVGNumber, SVGLength) to the new types (e.g., SVGAnimatedAngle, SVGAnimatedNumber, SVGAnimatedLength). Removed specific access to animated values from SVGPaint and SVGColor as the animated values of these properties are available from the override style sheet. Several bug fixes during this cleanup process where the DOM types did not match the types in the language.
  • DOM: Changed all indices to range from 0 to nItems-1, rather than 1 to nItems, to conform to the way DOM numbers its indices, including interfaces SVGList, SVGPath and SVGTextContentElement.
  • DOM: Added DOMException NO_MODIFICATION_ALLOWED_ERR for all attributes which are not readonly in case an attempt is made to change these attributes when the underlying node is readonly.
  • DOM: Moved DOM attribute "className" (corresponds to XML attribute 'class') into interface SVGStylable as it is available the same places the 'style' attribute is.
• Changes to Basic Data Types and Interfaces
  • Added a new section, Recognized color keyword names, which lists the expanded list of (147) color keywords, expected to be compatible with CSS3.
  • Under the definition of <color>, included a note saying that any of the user interface / system color keywords names from CSS2 can also be used.
  • DOM: Changed attributes on SVGTests to be an SVGList so that it is possible to access the individual entries in the list. Also, added a hasExtension() method to match the core DOM call hasFeature().
  • DOM: Changed the method names for SVGList from 'insertBefore()', 'replace()', 'remove()' and 'append()' to 'insertItemBefore()', 'replaceItem()', 'removeItem()', and 'appendItem()' in order to purposely avoid using the same method names as the Node interface in DOM since the corresponding methods on SVGList take different parameter lists than Node.
• Changes to Document Structure
  • Changed the description of the 'use' element to say that a 'use' is rendered as if it were replaced by a 'g' rather than an 'svg'. The new description eliminates problems in the areas of undesirable clipping and undesirable redefinition of CSS units which existed in previous versions.
  • Added a paragraph to the description of the 'image' element to make clear that raster images are fitted into the region (x,y) to (x+width,y+height) and that SVG files are processed using the standard rules for establishing a new viewport.
  • Changed 'system-required' to 'requiredFeatures' and defined the attribute to indicate whether the specified list of features is supported by the user agent. Added 'requiredExtensions' to indicate whether the given list of extensions is supported by the user agent.
  • Renamed 'system-language' to 'systemLanguage' to match the upcoming change with SMIL-Boston. Copied the description for this attribute from the latest SMIL-Boston draft.
  • Added a note indicating what happens if an event attribute is assigned to an element referenced directly or indirectly via a 'use'.
  • Added a paragraph to the description of the 'use' element to talk explicitly about how the 'visibility' property inherits into the referenced content of the 'use'.
  • Added an additional paragraph to description of 'externalResourcesRequired' to caution generators of SVG against setting this attribute to 'true' on the outermost SVG element as that might preclude progressive rendering of the content.
  • DOM: Added 'instanceRoot' and 'animatedInstanceRoot' to SVGUseElement and two new interfaces, SVGElementInstance and SVGElementInstanceList, to allow handling of events assigned to elements references by a 'use' element.
• Changes to Styling
  • Added a bullet saying that any of the user interface / system color keywords names from CSS2 are supported by SVG.
  • Major changes to this chapter to reflect the change from the two-grammar approach in the March 3 spec into a single, consolidated grammar which allows styling either using CSS or via corresponding XML attributes. The discussion now talks about properties in general and the two ways of expressing these properties: via XML "presentation attributes" or CSS style declarations.
  • Included simple examples of styling using an XSL external style sheet and styling using a CSS external style sheet. Revised the example of an internal CSS sheet.
  • Changed the section titled "Default style sheet" to "User agent style sheet" and clarified that the user agent style sheet shall only have the initial values specified in this specification when rendering on visual media.
• Changes to Coordinate Systems, Transformations and Units
  • Created a new section, 7.13 Establishing a new user coordinate system via object bounding box, that explains the rules for when coordinates are relative to an object bounding box. Consolidated various descriptions that used to be scattered about the specification for the exact rules concerning the computation of the bounding box and added a clarification of how bounding box works on 'text' elements.
  • Due to implementation difficulty and performance implications, removed the ability to use unit identifiers within a 'transform' attribute.
• Changes to Paths
  • Minor bug fixes to BNF for path data.
  • Changed the name of attribute 'length' to 'pathLength' to avoid DOM conflict with the 'length' DOM attribute that exists on the Node interface.
  • DOM: Major changes to the DOM for path segments. Now, SVGPathSeg is a base interface, with a different interface defined for each of the path segment types, such as SVGPathSegMovetoAbs. SVGPathElement now contains factory methods for creating each of the path segment types.
• Changes to Basic Shapes
  • Minor fixes to the BNF for the 'points' attribute for 'polyline' and 'polygon'.
  • Changed the rules for negative values for rx/ry on 'rect', r on 'circle' and rx/ry on 'ellipse' elements to be consistent with the treatment of inappropriate negative values in the rest of the spec. Now, negative values are an error.
• Changes to Text
  • Added new element 'glyphRun' to allow for a list of glyphs with different rendering order versus search/selection order. This feature addresses various internationalized text requirements.
  • Added attribute 'textLength' on 'text', 'tspan', 'tref' and 'textPath' elements to provide an option for an author to indicate the expected length which a given text string is supposed to take up.
  • Added new attribute 'lengthAdjust' to allow a choice between two methods for fitting text to a particular textLength: either just adjust the text advance values, or also stretch/compress the glyphs.
  • Added attribute 'method' to 'textPath' to allow an option to warp/stretch text-on-a-path. This facility will make cursive/script fonts (e.g., Arabic) stay connected when rendered along a path.
  • Added attribute 'spacing' to 'textPath' to allow an option for user agents to apply algorithms to make the rendered results as visual pleasing as possible.
  • Added clarification on objectBoundingBox on 'text' elements, documenting that the bounding box covers the entire 'text' element even when the effect is specified on a 'tspan' within the 'text' element.
  • Expanded the description of 'text-decoration' to describe explicitly how decorations are to be rendered and which properties are used to render the decorations. Added an example to illustrate the rules.
  • Fixed bug in spec where the default values for 'x' and 'y' on 'tspan' were defined as zero. The intent all along has been that a 'tspan' continues at the current text position from the previous character. As a result, there is new wording for what happens when any of the attributes 'x', 'y', 'dx', 'dy' and 'rotate' are not provided.
• Changes to Painting: Filling, Stroking and Marker Symbols
  • Changed the initial value for 'fill' from 'currentColor' to 'black' due to feedback from implementers and test developers that 'currentColor' does not have a real initial value, thus causing any SVG file that uses the initial value to have unknown rendering.
  • For various properties defined in this chapter, specified what happens when negative or zero values are supplied for items that represent lengths, distances or percentages. Typically, negative values are an error and positive values cause the item either to not be rendered or to fallback to some default rendering.
  • State explicitly that a zero stroke-width disables painting of the stroke.
  • Changed the description of how to render 'marker' elements to improve clarity and fix errors in the description. The order of the tranformations is described differently, particularly how (refX,refY) are factored in.
  • Changed the initial value for 'stroke-miterlimit' to 4 (instead of 8) as this better matches current industry practice and publishing industry guidelines.
  • Moved the 'display' property from the Styling chapter into this chapter, and then moved both the 'display' and 'visibility' properties into their own section entitled "Controlling visibility". Added a short discussion of the differences between these two properties.
  • Fixed bugs in definition of 'visibility' property. This property, which we share with CSS2, had been defined as inheritable, but the property is not inheritable. Also, the initial value was set incorrectly (should be 'inherit').
  • Added 'collapse' keyword to 'visibility' property to match CSS2. 'collapse' is defined in CSS2 to mean the same as 'hidden' for everything but tables.
  • Added clarification notes on the 'visibility' property about how invisible 'tspan' elements still take up space and how invisible objects still might receive events, depending on the value of property 'pointer-events'.
  • Included a detailed description of the two options for 'fill-rule' and included pictures illustrating the concept.
• Changes to Color
  • DOM: Changed the name of CSSColorProfileRule to SVGColorProfileRule as it directly inherits from interface SVGCSSRule, not CSSRule. As future version of the CSS OM evolve, this can be renamed to something like CSSColorProfileRule and the current name can be deprecated.
  • DOM: Added a note that SVGColorProfileRule that support for it is only required for implementations that support CSS.
  • DOM: Added DOM interfaces corresponding to elements 'color-profile' and 'color-profile-src'. Factored out SVGRenderingIntent into a separate interface that is shared between SVGColorProfileElement and SVGColorProfileRule.
• Changes to Gradients and Patterns
  • Changed the default for gradientUnits and patternUnits from 'userSpace' to 'userSpaceOnUse' after implementation feedback about difficulty achieving fast performance with 'userSpace'. The decision was that the default needs to be something with good performance characteristics.
  • Changed the description of 'linearGradient' to say if x1=x2 and y1=y2, then the gradient is rendered as a solid color matching the last gradient stop.
  • Changed the description of 'radialGradient' to say if r=0, then the gradient is rendered as a solid color matching the last gradient stop.
  • Clarified the behavior of linear/radial gradients in object bounding box space as being rendered perpendicular/circular relative to object bounding box space, which will result in non-perpendicular/elliptical results if the bounding box is not square in user space.
  • Clarified that the gradientTransform and patternTransform matrices are inserted immediately to the right (i.e., post-multiplied) to the transformation matrix caused by 'gradientUnits' or 'patternUnits'.
  • Changed the default values for fx/fy on radial gradients from "50%" to "same as cx/cy".
  • Added a 'spreadMethod' attribute to radial gradients for consistency with the specification for linear gradients.
  • Fixed bug introduced in April 13 spec where default value on y2 in 'linearGradient' was erroneously set to "100%" instead of the correct value of "0%".
• Changes to Clipping, Masking and Compositing
  • Changed the default for clipPathUnits and maskUnits from 'userSpace' to 'userSpaceOnUse' after implementation feedback about difficulty achieving fast performance with 'userSpace'. The decision was that the default needs to be something with good performance characteristics.
  • Masks now use both the luminance of the color channels and the alpha channel. Previously, there was a very arbitrary and confusing set of scenarios when the luminance of the color channels were used in a mask. Now, the luminance is used always. This change makes for a more consistent rendering model and better matches industry practice.
  • Changed the initial value on 'clip-path' from "see prose" to 'none'. There is no actual behavioral change with this change; the old prose described the same affect as 'none'.
  • Explicitly stated that if clipPathUnits="objectBoundingBox", the 'transform' attribute on the 'clipPath' element is ignored as the coordinate system has become defined relative to the bounding box on the referencing element.
  • Added clarification to the description of 'clip-rule' indicating that the property only applies to shapes within a 'clipPath' element.
• Changes to Filter Effects
  • Added attribute primitiveUnits as a separate attribute from filterUnits so that different coordinate systems can be used to specify the filter region versus the length and coordinate values within the filter primitives. For example, the filter region might be specified relative to the object bounding box, but the filter primitives might be specified relative to the current user coordinate system. The separation is particularly useful if applying a common filter effect to multiple text strings, where the filter effect region is defined in terms of object bounding box but the primitives have a common light source position.
  • Modified the coefficients for 'luminanceToAlpha' in feColorMatrix as the previous coefficients were incorrect. (The old formulas were based on NTSC colors rather than sRGB).
  • Changed the types of k1,k2,k3,k4 on feComposite to be numbers and removed the erroneous comment about only 0 and 1 being the only valid values.
  • Removed attribute resultScale from feDiffuseLighting as it did not really address the presumed end user needs, and those needs can be accomplished in other ways.
  • Added attribute 'bias' to feConvolveMatrix, which allows a constant value to be added to each color channel after application of the kernel.
  • Added attribute 'preserveAlpha' to feConvolveMatrix, which provides an option to specify whether the kernel should be applied to all channels or just the color channels.
  • Added attribute 'limitingConeAngle' to feSpotLight, to allow for the effect of a spotlight to be restricted to a particular conic area.
  • Minor updates to code for feTurbulence after actual compilation and use and verification across different implementations.
  • Changed the default for filterUnits and primitiveUnits from 'userSpace' to 'userSpaceOnUse' after implementation feedback about difficulty achieving fast performance with 'userSpace'. The decision was that the default needs to be something with good performance characteristics.
  • Added a 'discrete' option to feComponentTransfer for a step function, which is a common way to achieve a posterizing effect.
  • Changed attribute 'lightColor' in 'feDiffuseLighting' and 'diffuseConstant' into property 'lighting-color' for consistency so that everything that defines a color value is done via a property. This also provides consistency with 'flood-color' in 'feFlood'.
  • Change 'diffuseConstant' and 'specularConstant' to take any non-negative value instead of just values in the range of 0 to 1. This change coincided with dropping the 'resultScale' attribute for 'feDiffuseLighting'.
  • DOM: Changed the name of DOM attribute "in" to "in1" since "in" is a keyword and cannot be used as a DOM attribute name.
• Changes to Interactivity
  • Replaced attribute 'enableZoomAndPanControls="true|false"' with attribute 'zoomAndPan="disable|magnify|zoom"', with the default being 'magnify'. This new formulation and new default helps alleviate unexpected behavior that was occurring when filters and gradients were specified using CSS units and the user zoomed in on the graphic.
• Changes to Scripting
  • Fixed bugs in the scripting example.
• Changes to Animation
  • Added an 'mpath' child element to 'animateMotion' so that the motion path can be defined via a reference to a previously defined 'path' element.
  • Added a few sentences under 'animateMotion' to clarify that the motion animation provides a transformation that is supplemental to any transformations from the elements 'transform' attribute or any animations on the 'transform' attribute.
  • Fixed bugs in the DOM animation example.
• Changes to Fonts
  • Made it possible for 'font-face' to be a child of 'font' so that a single 'font' element can contain all information necessary for other documents and other languages to make use of the font.
  • Moved many font-descriptor attributes from the 'font' element to the 'font-face' element, such as 'font-size', font-weight', 'cap-height', etc. This change reduces redundancy in the language.
  • Minor modifications to the list of descriptors in 'font-face' to be the union of the font descriptors from CSS2 and any new font descriptors that are emerging from the work on XSL.
  • Made the 'unicode' attribute on the 'glyph' element #IMPLIED to allow for definition of glyphs which do not have corresponding code points in Unicode. Such glyphs can only be accessed via the 'altGlyph' facility.
  • Added class/style/presentation attributes to the 'font' element per decision that all container elements would allow all properties.
  • Clarified that font metrics and the initial coordinate system for glyphs is based on the CSS2 model of an em square. Also, clarified that the coordinate system for SVG fonts has the Y axis pointing up to match common practice with other font formats.
  • Changed the default for attribute unicode-range from "U+0-7FFFFFFF" to "U+0-10FFFF", as no XML characters beyond that range.
• Changes to SVG DTD
  • Substantial changes to the DTD to accommodate the consolidation of Stylable SVG and Exchange SVG (from the March 3 spec) into a single language which has both XML "presentation attributes" and the ability to style with CSS (i.e., a 'style' element and a 'style' attribute). Instead of three DTD files (shared, stylable, exchange), there is now only one DTD file. All of the conditional logic based on the names "SVGStylable" versus "SVGExchange" from the March 3 specification has been removed
  • Substantial editorial cleanup of the DTD, including reordering the element definitions to match the order in which they appear in the spec, grouping element definitions by chapter, adding a table of contents with links to each section of the DTD, comments over each section of the DTD, new names for various entities, etc.
  • Substantial cleanup of the list of "presentation attributes" on the various elements. The rule is that if a given attribute collection might apply to a given element or any of its descendants, then that collection of presentation attributes is available on the given element. Defined a new entity PresentationAttributes-All which contains a complete list of the presentation attributes. All container elements and the 'use' element now reference this new entity so that all presentation attributes are available for these elements.
  • Unified the content models for 'mask', 'pattern', 'symbol', 'marker', 'glyph', 'missing-glyph' and 'a' for greater consistency and to give implementers a greater ability to share code.
  • Added 'desc' and 'title' to 'tspan', 'tref', 'textPath', 'linearGradient', 'radialGradient' and 'filter' for more DTD consistency.
  • Allow a 'metadata' sub-element wherever a 'desc' or 'title' can go so that metadata can be specified locally for each distinct container and graphics element.
  • Made changes to ensure that attribute 'class' existed everywhere where attribute 'style' existed, which means adding 'class' to 'feFlood', 'glyph' and 'missing-glyph'.
• Changes to SVG DOM
  • Added a section on "Invalid values" to clarify what happens when an invalid value is assigned to an attribute.
• Changes to IDL
  • The IDL reflects all of the changes to the DOM mentioned in other parts of this change history. Most significantly, the IDL reflect changes to accommodate the consolidation of Stylable SVG and Exchange SVG (from the March 3 spec), such as the removal of all #ifdef STYLABLESVG and #ifdef EXCHANGESVG.
• Changes to Java language DOM binding
  • To accommodate the consolidation of Stylable SVG and Exchange SVG (from the March 3 spec), there is now only a single Java binding instead of two separate ones.
  • Various fixes to the Java binding based on reports from implementers have been incorporated into the Java binding that accompanies this draft.
• Changes to ECMAScript language DOM binding
  • To accommodate the consolidation of Stylable SVG and Exchange SVG (from the March 3 spec), there is now only a single ECMAScript binding instead of two separate ones.
  • Added constants to the ECMAScript language binding as is now done with other W3C specifications.
• Changes to Conformance Criteria
  • Modifications associated with replacing the two-grammar approach from the March 3 spec (i.e., Stylable SVG and Exchange SVG) with a single grammar approach which allows styling either using CSS or via corresponding XML attributes. Now, all Conforming SVG Viewers must support the ability to assign styling properties via the XML "presentation attributes", and any CSS-enabled viewer must support the ability to assign styling properties via CSS syntax in the form of CSS style sheets or style rules within a 'style' attribute.
• Changes to Minimizing SVG File Sizes
  • Updated the gzip compression table using five SVG files from the 20000608 test suite.
• Changes to References
  • Moved Authoring Tools Accessibility Guidelines into the normative section as these guidelines are now a Recommendation and conformance to these guidelines is a requirement for authoring tools that are Conforming SVG Generators.