The original misleading post/question:
I looks like that if a tag contains Unicode characters the tag completion does not list it. If true, can we have support for Unicode aware completion everywhere? Would it be as simple as to just add the
uflag to the regular expressions involved in the tag/attribute/etc. completion functions?
Update: It seems I must have been misled somehow. I did some experiments and it seems to me now that tags that appears only in table cells are not showing up in the completion, nor are they showing up when listing all tags from templates. I will have to dig into what’s happening more further and let you know. Accidentally, the tags not showing up in both listings and completions are the only that have Unicode characters in them and are present only in table cells.
Update 1: Confirmed that if tag appears only in cells of some table then it’s not listed in {tag}. If I place the same tag elsewhere out of a table on the page, it then appears in {tag}. Is it a bug? Can it be fixed, please?
Update 2: OK, I created the test page you see below and it’s quite confusing and against my natural expectations about how it should in fact work:
#<AAA page>
Works as expeced.
# #<AAA heading 1> Does not work
## #<AAA heading 2> Does not work
Paragraph. #<AAA paragraph> Works, but misplaced.
- list item #<AAA list item> Works.
- [x] task #<AAA task> Works.
- #<AAA sub-list item> Works, byt it's page does not show anything.
Column1 | Column2
-|-
#<AAA table cell C1> Does not work | #<AAA table cell C2> Does not work
This is what I finally got:
| ref | tag | name | page | parent |
|---|---|---|---|---|
| AAA list item:item | tag | AAA list item | Tests | item |
| AAA page:page | tag | AAA page | Tests | page |
| AAA paragraph:page | tag | AAA paragraph | Tests | page |
| AAA sub-list item:item | tag | AAA sub-list item | Tests | item |
| AAA task:task | tag | AAA task | Tests | task |
As you can see, for two kinds of objects the tag is missing: for the headings and for the table cells.
Other flaws: for the sub-list item the tag’s page (the one with the red pin you get if you click on the tag) does not refer to anything! So there may be some issues with nested lists, I guess.
And, the most important, the paragraps are probably not counted as standalone objects and tags placed in paragraps have page as their parent. I would prefer to see rather more hieararchical approach to this, not only because I like to write my tags directly in the text while typing and therefor I would like to refer to the paragraphs (or sections) rather than to whole page that may be very lengthy, but because it feels very natural to me to refer into hierarchy while the nature of the text is, indeed, hierarchical. 
I wonder if this could be improved (at least for the sections and paragraphs). What do others think about it? Please, share your opinion. Thank you.