option every time we might want to allow or disallow new output. Adds two new
options:
- `squelch-id` (default **no**) will provide tags during Tidy's output that
can be used to silence warnings. For example, `MISSING_ENDTAG_OPTIONAL`
will be shown after warnings of that type. Then in the future, the user can
use...
- `squelch` (default NULL) takes a list of message identification tags.
Messages of this tag type will then be muted from output.
This gives the user great control over hiding things that he or she doesn't care
about seeing. However, muted errors/warnings still count toward error summaries.
If we merge this, then TidyShowMetaChange and TidyWarnPropAttrs are candidates
for removal (using the deprecation mechanism Tidy now has, these will continue
to work, though).
626375346d