Letters A to Z and digits are restyled. Other characters stay as they are.
Use sparingly. Styled text is made of special symbols, not real bold or italic. Screen readers may read it letter by letter or skip it, and it may not be found by search. Avoid it for links, hashtags, names and anything important, and keep it to a few words such as a heading. Some styles show empty boxes on devices whose fonts lack those symbols.
Works by swapping letters for matching Unicode symbols, so it needs no server and your text never leaves your browser. Pasted results look the same on platforms that support these symbols, but some apps filter or replace them.