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Overview
HTML5 now allows <svg> and <math> markup with an HTML document without depending on external namespaces (decent overview here). Both have their own alt-attribute analogs (see below) which are effectively ignored by today's screen-reader software. Thus, these elements are inaccessible to blind users.
Are there plans to implement a standard alt-text convention for these new elements? I've scoured the docs and have come up dry!
Futher Details
Regarding SVG: an SVG's alternate text could be considered the contents of the root title or desc tag.
<svg> <title>An image title</title> <desc>This is the longer image description</desc> ... </svg> I've found one screen-reader which reads it as such, but is this standard? Previous methods of inserting SVG also had accessibility issues since <object> tags are treatedly inconsistently by screen-readers.
Regarding MathML: MathML's alternate text should be stored in the alttext attribute.
<math alttext="A squared plus B squared equals C squared"> ... </math> Since screen readers do not seem to acknowledge this, the math-rendering library MathJax inserts text into an aria-label attribute at run-time.
<span aria-label="[alttext contents]">...</span> Unfortunately NVDA, JAWS, and others do not reliably read these labels yet either. (More on WAI-ARIA)
Regarding both: lacking success with the largely-unsupported ARIA attributes, I tried using title attributes. These also seem to be ignored on these "foreign" HTML elements.
Wrap-Up
More than a quick hack, I'm looking for the recommended way to place alternate-text on these new HTML elements. Perhaps there is a W3C spec I'm overlooking? Or is it still just too early in the game?
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Including an SVG in an img tag is no different than including a regular image–always use an alt tag for SVGs that are important!
Using the <img> Tag For basic, uncomplicated, or decorative images, use the <img> tag and reference the SVG as a file. This pattern should render lighter and faster pages overall (versus inline SVGs) and allow for easier maintenance on SVGs that you use in multiple places.
This <svg> element contains a red circle and has a role attribute to indicate that it contains an image. But because the <svg> element doesn't have alternative text, people who use assistive technologies won't know what image it represents.
Add alt text all non-decorative images. Keep it short and descriptive, like a tweet. Don't include “image of” or “photo of”. It's not necessary to add text in the Title field.
After some digging, I found some somewhat official recommendations. Unfortunately, most are not functional at this point in time. Both the browsers and the screen readers have a lot of to implement before Math and SVG can be considered accessible, but things are starting to look up.
Disclaimer: the below recommendations are what I have gleaned over the past few months of coding. If something is dead wrong, please let me know. I will try to keep this up to date as browsers and AT software progresses.
Recommendation
Use role="math" along with an aria-label on a surrounding div tag (see docs). The addition of tabindex="0" allows screen readers to focus specifically on this element; this element's aria-label can be spoken using a special key shortcut (such as NVDA+Tab).
<div role="math" tabindex="0" aria-label="[spoken equivalent]"> <math xmlns="http://www.w3.org/1998/Math/MathML"> ... </math> </div> Limitations/Considerations
aria-label (and less importantly role="math").aria-label here and here.div or span tag seems unnecessary since math is a first-class element in HTML5.alttext tag.References
Recommendation
Use top-level <title> and <desc> tags together with role="img" and aria-label on the root SVG tag.
<svg role="img" aria-label="[title + description]"> <title>[title]</title> <desc>[long description]</desc> ... </svg> Limitations/Considerations
<title> and <desc> tags, which is probably undesirable. However, NVDA, JAWS, and WindowEyes will read the aria-label when the element also contains role="img".<title> tag will become the browser page's title, which will be read by the screen reader.References
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