This command is meant to do the same as `insert-char' does.

The only issue is that the built-in `ucs-names' variable, which is
offered for completion, includes around 40000 entries. Maybe there
should be a way for the user to turn off the Unicode ranges she's never
interested in (see the division of ranges in the `nxml-unicode-blocks'
variable).  In the included screenshot, I've already disabled some
ranges that aren't interesting for me - my font doesn't have glyphs for
a large portion of these.

Another issue I've found when shortly examining the Unicode table is
that it provides these three categories:

1. Plain letters,

2. Composition characters, like COMBINING GRAVE ACCENT, COMBINING ACUTE
ACCENT etc.,

3 Plain letters pre-combined with the above composition chars.

So maybe the user should decide if she prefers to have 1+2 or 1+3 or
1+2+3, the latter option significantly increasing the number of
completion candidates (by around 2500).

    Oleh