The TeX Catalogue OnLine, Entry for subscript, Ctan Edition

Provides the \textsubscript command.

Provides a command \textsubscript, which is a modified version the command \textsuperscript that's part of LaTeX. The command is also (now) provided by the fixltx2e package distributed with LaTeX itself; if you are running a LaTeX distribution no earlier than 2005/12/01, you will have a more satisfactory means of using the command.

Subscript is one of a series of fragments designed for use by package writers and others.

The author is Robin Fairbairns.