Can a combining character be used alone in Unicode?

Question

Let\'s take COMBINING ACUTE ACCENT, for example. Its browser test page does include it alone in the page, but it reacts in a strange way: I can\'t select it with my mouse, a

Answer 1

Yes, a combining character alone is a valid Unicode string (even though its behaviour may be weird without a base character). Section 2.11 of the Unicode Standard emphasises this:

In the Unicode Standard, all sequences of character codes are permitted.

The presentation of such strings is described in D52:

• There may be no such base character, such as when a combining character is at the start of text or follows a control or format character [...] In such cases, the combining characters are called isolated combining characters.

• With isolated combining characters or when a process is unable to perform graphical combination, a process may present a combining character without graphical combination; that is, it may present it as if it were a base character.

However, if you want to display a combining character by itself, it is recommended that you attach it to a no-break space base character:

Nonspacing combining marks used by the Unicode Standard may be exhibited in apparent isolation by applying them to U+00A0 NO-BREAK SPACE. This convention might be employed, for example, when talking about the combining mark itself as a mark, rather than using it in its normal way in text (that is, applied as an accent to a base letter or in other combinations).

Answer 2

Also, a dotted circle ◌ (U+25CC, ◌) character can be used as a base character.

Source: https://en.wikipedia.org/wiki/Dotted_circle