What small caps are
A small capital has the shape of an uppercase letter at roughly the height of a lowercase one. Typographers have used them for centuries for acronyms, headings and opening lines, because they emphasise text without the visual noise of full uppercase.
What this tool produces is not true typographic small caps. A layout program generates those from the font itself; here you get separate Unicode characters that resemble small capitals. The upside is that they survive copy and paste anywhere. The downside is everything below.
Where these characters come from
They are not from a decorative block. They come from the International Phonetic Alphabet — Unicode encoded them because linguists needed them to transcribe speech sounds, which is why they are scattered across the Phonetic Extensions and Latin Extended-D blocks rather than sitting in one tidy range.
That origin explains the main quirk: the set is incomplete.
The missing letter
There is no small capital X in Unicode. Every other letter of the alphabet has one; X was never encoded because phoneticians had no use for it.
A lowercase x stands in here, which is the usual convention and the closest
match in height. The tool says so explicitly under the style, so you find out
before pasting rather than after.
Q is the opposite curiosity: its small capital ꞯ does exist, but it arrived
late (Unicode 9, in 2016), so older systems may show an empty box for it even
when the rest of the text renders fine.
Upper and lower case
Both fold to small capitals. Whether you type PEINAN or Peinan, the result
is ᴘᴇɪɴᴀɴ. That uniform block is almost always what people want from small
caps — mixed heights defeat the point.
Before you use it
Screen readers treat these as phonetic symbols rather than letters. They may spell them out, announce them with unfamiliar names, or skip them.
They work well as a short flourish. Avoid them in your real name, in long-form text, and in anything that has to be readable with a screen reader.