Done. However, I'm not a really good writer of this kind of documentation... any comments and/or improvements are welcome :)
Couple of minor comments (I've used lines from the Geany.txt diff to identify them, hence the + signs.):
+Tags for each document are parsed whenever a file is loaded or saved, and
Just replace the "or" with a comma.
+possibly when modified (see *Symbol list update frequency* preference in the
Since the default is to update on modify, I'd leave the "possibly" out.
+ current document. The smaller is the delay the more up-to-date is the + symbol list (and then the completions); but rebuilding the symbol list + has a cost in performance, especially with large files.
Leave out both "is" in the preceding sentence, not needed, add a comma after delay.
+ + The default value is 250, which means the symbol list will be updated at
Add milliseconds after 250
+ most 4 times per second, even if the document changes continuously.
Single digits should be spelled out so "four".
Cheers Lex