Why small text survives copy and paste
Bold, italic and small caps on a web page are normally properties of a font, applied with CSS or a word-processor style. Paste that text into a username field or a chat box and the styling is stripped, because those fields accept plain characters only. Unicode small text sidesteps that by using characters whose glyphs already look small: the small capital H is code point U+029C, a different character from H, and it keeps that shape wherever plain text goes.
Most of these glyphs were encoded for linguists and mathematicians, not for styling. The small capitals sit in the IPA and phonetic extension blocks, where they mark particular speech sounds. Superscript and subscript digits were added for chemistry, footnotes and formulas. Using them for a decorative bio is a side effect of their existence, which is why the sets are uneven and why some software treats them oddly.
What each style maps
Small caps maps all 52 upper- and lower-case ASCII letters, so HELLO and hello both produce the same result. There is no small capital in the map for q or x: q is replaced with an o with ogonek that reads as a small Q, and x is left as the ordinary letter. Everything else, including digits, spaces and punctuation, passes through untouched.
Superscript maps the 26 lower-case letters, folding capitals to lower case first, along with the digits 0 to 9 and the symbols + - = ( ). Unicode has no superscript q, so the tool uses a Canadian syllabics character of the same shape as a stand-in. Subscript is the thinnest set: 17 letters, the same digits and symbols, and nothing for b, c, d, f, g, q, w, y or z, which stay as typed and produce mixed words such as Wₒᵣₗd for World.
Where the styled text does not work
Handles and usernames are the most common failure. Many services restrict the handle itself to ASCII letters, digits and the _ character while accepting almost anything in the display name, so paste into the display-name field when the handle field rejects it. Some platforms also normalise or reject look-alike characters in names to limit impersonation, and that policy can change without notice.
Search and filtering are the second problem. A search for hello does not match the small-caps version, because case folding and search engines treat small capitals as separate letters, so a styled display name is effectively unsearchable. The same applies to find-in-page, spreadsheet filters and database queries. If people need to look you up by name, keep a plain-text copy of it somewhere visible.
Fonts matter too. A device without a font that covers the phonetic extension blocks shows empty boxes instead of letters, and a device that borrows glyphs from a second font shows uneven weights and baselines. Current phones and desktop systems cover the small-capital range well. Some email clients and older embedded devices do not.
Accessibility, and when to use real small caps instead
Screen readers handle these characters inconsistently. Some announce the small capitals as the intended letters, some read each one by its Unicode name, and some skip them, so a sentence in small text can be unreadable to a blind user. Keep styled text to decoration and short flourishes, and never put instructions, prices or a contact method in it.
For a website or document you control, use real typography: the CSS declaration font-variant: small-caps renders proper small capitals from the font, superscript and subscript have their own HTML elements, and the text underneath stays plain, searchable and screen-reader friendly. Unicode small text is for the places where you cannot control the styling: a bio field, a game name, a comment box. For a blank name rather than a styled one, the invisible character tool covers that trick.