W3C spec syntax

Hi all,

As part of my continuing WPD articles work, I use W3C specs to get
information about objects, methods, and properties. These specs include
details that are laid out in a specific but somewhat obtuse syntax. For
example, in the masking spec
https://dvcs.w3.org/hg/FXTF/raw-file/default/masking/index.html
there's this

<basic-shape><https://dvcs.w3.org/hg/FXTF/raw-file/default/masking/index.html#ltbasic-shapegt>
 | <clip-source><https://dvcs.w3.org/hg/FXTF/raw-file/default/masking/index.html#ltclip-sourcegt>
|
none

which is clear enough: use one of the three values. And there's this

[ stretch | repeat | round | space ]{1,2}

which is still fairly clear: use either one or two of the grouped words,
all optional. But then there's this

<‘mask-box-image-source<https://dvcs.w3.org/hg/FXTF/raw-file/default/masking/index.html#mask-box-image-source>
’> || <‘mask-box-image-slice<https://dvcs.w3.org/hg/FXTF/raw-file/default/masking/index.html#mask-box-image-slice>
’> [ /<‘mask-box-image-width<https://dvcs.w3.org/hg/FXTF/raw-file/default/masking/index.html#mask-box-image-width>
’> | / <‘mask-box-image-width<https://dvcs.w3.org/hg/FXTF/raw-file/default/masking/index.html#mask-box-image-width>
’>? /<‘mask-box-image-outset<https://dvcs.w3.org/hg/FXTF/raw-file/default/masking/index.html#mask-box-image-outset>
’> ]? || <‘mask-box-image-repeat<https://dvcs.w3.org/hg/FXTF/raw-file/default/masking/index.html#mask-box-image-repeat>
’>

which is... not so much: there's one vertical bar, two vertical bars,
question marks, etc. It's kind of hard to interpret. This is just one
example; I often run into similarly complex syntax in W3C specs.

I've poked about the web but haven't found a "syntax syntax" guide. Does
anyone know if there is such a thing, either from the W3C or within the WPD
community?

Thanks,
Dave Gash