This section and its subsections are informative (non-normative).
Although a WebCGM metafile is a binary file
format, it has a number of features that enable accessibility of WebCGM metafile content
to be improved. 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,
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 editors.
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 release of WebCGM, if indicated by new requirements gathering.
It is recommended that WebCGM viewers should provide optional keyboard methods (e.g., the TAB key) 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. However[dW1] , the private-namespace extension feature of the XCF can be used to improve the situation. For example, authoring tools and viewers could define namespace attributes such as kbaccess:nav-next, kbaccess:nav-prev APS (which would behave as the similar standard SVG nav-next and nav-prev 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 '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 should provide the option for users to define these descriptive attributes. It is recommended that WebCGM viewers should provide users the option to be informed of the presence of these attributes, and the option subsequently to read them or not.
For the title/desc component of hyperlinks, it is recommended that viewers provide the option to read the attribute to users, and possibly offer the choice then whether to execute the link or not[dW2] .
[dW1]I am not sure about this. At the end
of the day, navigation from object to object is not a use case for WebCGM, and it can not be used to understand the content of
Example: a typical parts catalog page, where the callouts are objects. Cycling through and reading the content loud would yield something like “1…24…43…3…8” and so on. Not really useful.
Suggestion: Let's stay with "...could be considered for a future release of WebCGM, if indicated by new requirements gathering."
[dW2]Same comment as above. This is not a use case for WebCGM as far as I can see. Let’s first gather the requirement that e.g. blind people have to be able to work with this before we define requirements/recommend extensions to viewer functionality.
We might think about an introductory statement like: WebCGM is intended for heavy industrial use, where certain capabilities of the user are required to do his job.
If this is politically correct, of course.