insert-char completion says no matches, but inserts character anyway?

Question

I'm using C-x 8 RET to insert a Unicode character. I enter the hex value -- for example, 201c -- and the minibuffer says "no matches". But if I just hit enter, the expected left double quote character “ gets inserted.

OTOH, if I type "left quot" or similar, the completion narrows the choices as expected, and I can use tab to complete LEFT DOUBLE QUOTATION MARK as expected.

I'm seeing similar behavior even when I start emacs with "-Q": there, I type "201c", hit tab -- it says no match, but if I hit enter, it inserts the character.

Why is the completion saying there's no matches, but hitting enter successfully finds the character?

Answer 1

You see No match when you hit TAB because there's no match for the text 201c using the completion-styles you have.

More importantly, C-x 8 RET matches character names, not code points. But if you hit RET to enter a code point, then its char is inserted.

See the doc of function insert-char (which is bound to C-x 8 RET). It says:

You can specify CHARACTER in one of these ways:

• As its Unicode character name, e.g. "LATIN SMALL LETTER A". Completion is available; if you type a substring of the name preceded by an asterisk *, Emacs shows all names which include that substring, not necessarily at the beginning of the name.

• As a hexadecimal code point, e.g. 263A. Note that code points in Emacs are equivalent to Unicode up to 10FFFF (which is the limit of the Unicode code space).

• As a code point with a radix specified with #, e.g. #o21430 (octal), #x2318 (hex), or #10r8984 (decimal).