html does not support table separator rows as Org mode does. Emacs org export
simulates rows as defined by separators by wrapping all the rows between 2
separators into a separate tbody. The html spec is fine with that [0] so we
follow.
[0] https://developer.mozilla.org/en-US/docs/Web/HTML/Element/tbody
- we can't just look at the len of the string (~ #bytes) - that breaks down for
tables containing characters consisting of multiple bytes. This handles
more (still not all) cases and is good enough for now
- add _ to allowed tag chars - also require space between headline and tags
- links (link itself, not the description) spanning multiple lines are not
supported - otherwise we would have to take care of splitting link and adding
indentation for org pretty printing - and that sounds like such an edge case
that it seems cleaner to forbid them
Also dismissed implementing colgroups for now - had it but didn't like the
added complexity for a very questionable benefit - i've actually never used
that feature of org tables...
