[Draft: 2006.08.31]

E. WebCGM accessibility

This section and its subsections are informative (non-normative).

E.1 Introduction

Although a WebCGM metafile is a binary file format, it has a number of features that enable accessibility of WebCGM metafile content. For example, graphical text is ideally stored as Unicode text strings within the metafile, but to handle cases where graphical text images are actually the result of other vector (e.g. stroking) or raster (e.g., bitmaps) graphics in the metafile, WebCGM has the attribute 'content' on the para and subpara objects, that gives the text-string equivalent of the rendered graphical text.

Features that are in the binary metafile itself will, unlike clear-text formats such as HTML, XML, and SVG, require the cooperation and intervention of the WebCGM authoring tools and viewers. Therefore, the discussions in the following sections are recommendations to builders of authoring tools and viewers.

E.2 Navigation order

By default, every APS (object or layer) in WebCGM is focusable. In this version of WebCGM, there is no facility to change the default focusability. Such a feature could be considered for a future version of WebCGM, if indicated by new requirements gathering.

It is recommended that WebCGM viewers offer a mode whereby, at user option, keyboard methods (e.g., the TAB key) allow users to cycle the focus through objects in document order.

In this version of WebCGM, there are no intra-metafile controls to alter the navigation order. In a scenario where such capability were required, the private-namespace extension feature of the XCF might be used to craft a solution.

E.3 ALT-like attributes

WebCGM contains some attributes that can be used like XHTML 'alt'.

• The 'content' attribute was mentioned in the previous section.
• The 'screentip' attribute is allowed on all objects (APS).
• The 'layerdesc' attribute is allowed on 'layer' APS types.
• On hyperlinks ('linkuri' APS attribute), the attribute components "Link Title" (in metafile instances) or 'desc' (in XCF instances) could be used like ALT, to describe the meanings of hyperlinks.

It is recommended that WebCGM authoring tools offer a mode whereby, at user option, the user may define these descriptive attributes. It is recommended that WebCGM viewers offer a mode whereby, at user option, users will be informed of the presence of these attributes, and the choice subsequently to read them or not.

For the title/desc component of hyperlinks, it is recommended that viewers offer a mode whereby, at user option, the viewer will read the attribute to users, and possibly offer the choice then whether to execute the link or not.

Note. It has been speculated whether the 'name' APS attribute has similar ALT-like application. It does not. The 'name' attribute has well-defined specific semantics, for navigation to a group of like-named objects.

E.4 Visibility and object reading

By default, objects which are not visible do not display tooltips (the 'screentip' APS attribute), may not be highlighted without making them visible, and may not be navigated to via the DOM or picture behaviors. It is recommended that WebCGM viewers offer a mode where, at user option, the 'visibility' attribute is ignored, for accessibility or debugging support.