Just like sed is a stream editor, ted is a token list editor.
Actually, it is not as powerfull as sed, but its main feature
is that it really works with tokens, not only characters. The
ted package provides two user macros: \Substitute and
\ShowTokens. The first is maybe the most useful: it performs
substitutions in token lists (even inside braces). The second
displays each token of the list (one per line) with its catcode
(in the list, not just the current one), and can be useful for
debugging or for TeX learners. Ted is designed to work well
even if strange tokens (that is, unusual {charcode, catcode}
pairs or tokens with a confusing meaning) occur in the list.