This is a new take on c8e2c17a that was reverted at da67bde61a due to entities no more recognised by the browsers. Corresponding thread on the mailing list: https://www.mail-archive.com/lyx-devel@lists.lyx.org/msg213179.html
This patch is a huge cleanup overall, by removing the distinction between HTML and XML entities (the latter arrived due to the DocBook support).
In InsetListingParams, I also changed the mechanism that relied on " to use an XML entity to be consistent with the rest of the code, mostly in case someone looks for HTML entities and wonders why they are still there.
It could be a part of the standard test suite, but it might be quite long to run.
This test ensures that the generated XHTML files are valid HTML5 files, i.e. should display fine in all browsers.
Also, perform the URL fixing magic for DocBook and XHTML.
As it was, it was impossible to enter e.g. "tel:" type links. Now
choosing the "Other" type just outputs the URL as given.
Also, the addition of "http" or "file" was not being done for
DocBook and XHTML. Now it is.
This adds a warning icon to either the tab header or the panel stack
entry item if a widget on the panel/stack has invalid content.
Particularly helpful to get aware of such content on other tabs/panes
than the one currently selected.
Before, there was always a space after the tag, even when there were no attributes. Now, the space is output conditionally, so that the output makes more sense.
Before, one space too many for the tag name (title), casting doubt on whether the code had this space hard coded or not:
<!-- Output Error: Unrecognised tag type 'para' for 'title ' -->
After, no such space:
<!-- Output Error: Unrecognised tag type 'para' for 'title' -->
Remove some special cases that I do not really understand and
streamline the cases.
Also make sure that there is only one code path for centering.
Fixes bug #12491.
Instead of having to add and individually test the versions to check
for, we store the current version and test on that with a specific
function isAvailableAtLeastFrom(package, year, month, day)
Currently only used for the LaTeX version, but could also be extended
for package versions.
