Like Unicode bold, this tool maps each letter onto the "Mathematical Italic" block — a set of slanted look-alike characters originally standardized for math variables — so the italic look is baked into the character itself instead of relying on an app's rich-text renderer. That's what makes it usable in plain-text-only fields like usernames, bios, or chat apps where markdown italics (like *this*) would otherwise just show literal asterisks. One quirk carried over from the math block: the lowercase 'h' uses a separate legacy Unicode symbol (the Planck constant symbol, ℎ) instead of the newer italic block, because that glyph was standardized earlier — this tool handles that exception automatically.
Markdown italics only render where the specific app parses that syntax — paste *text* like this into a plain field and you'll see the literal asterisks, whereas Unicode italic characters display as slanted text everywhere Unicode is supported.
Lowercase italic h uses an older, separately standardized Unicode symbol (originally for the Planck constant) rather than the newer math-italic block, since that specific glyph already existed — this tool maps it correctly so it still reads as italic h.
No — Unicode's math-italic block only defines letters, not digits, so numbers in your text are left unchanged rather than approximated with an unrelated symbol.