This is a little bit a hack, because by the time the separators are
added, it is not clear, if the following section is empty, therefore
we need to parse the content of the following section and eval the
expressions to find out, if this is empty
Remarks:
- catch all exceptions when eval'ing statusline
- make sure, that the seperators are highlighted
even when skipping empty regions (highlight group
names need to be adjusted)
- if a section is defined as empty, it will be removed completly from
the statusline. This means, it won't be called on the next update
and may not refresh properly (e.g. when the whitespace check
triggers, therefore, the whitesapce extension has to call an
explicit redraw whenever it is supposed to be refreshed)
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