documentation of brace expressions in zshcompwid(1) man page

The documentation of brace expressions in the zshcompwid(1) man page
is incomplete concerning character classes.

For instance, what would m:{[:alpha:]}={[:digit:]} give?

Does this mean that for any alphabetic character, the match pattern
is broadened with any digit?

If this is the case, why would m:{[:lower:]}={[:upper:]} give only
the uppercase counterpart? Or is this an exception, i.e. both are
expanded as ranges? But how are these ranges determined? e.g. what
if there is no uppercase counterpart? For instance, in ISO-8859-1,
ÿ (code 255) does not have an uppercase counterpart.

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Vincent Lefèvre <[email protected]> - Web: <https://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / Pascaline project (LIP, ENS-Lyon)