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, requiredrequire 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 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
the illustration.
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.
[dW3]Nothing, IMHO.
General
comment:
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.