Regarding, [string.capacity], Alisdair points out that "'size of' may also refer to the result of the 'sizeof' operator, so I would use 'length' instead, as we define both."

Daniel then points out:
"I think that using the notion of "length" still makes the meaning unclear, it is now like a recursive definition, because length() is defined in terms of size(), not vice versa. What about:

"The largest possible number of char-like objects that can be [stored in] a [basic_string]."

(I edited the above to adapt their suggestions from basic_string_view to basic_string.)