Good point about reading docs, but about doing what they claim, to be fair, the String module contains functions to deal with UTF-8 encoded strings, as the name suggests, not with arbitrary binaries.

As recent posts have shown, bitstrings vs. binaries vs. strings can be a tricky topic that deserves attention. But I don’t think this is a case of surprising behavior of the String module

Just checked in IEx:

iex> h String.length
...
Returns the number of Unicode graphemes in a UTF-8 string.
...

So TIL to always look at the doc for obviously named functions to be sure that they do what they claim we might think they do.. (edited)

This is more about wrong assumptions than library docs IMO.

People are used to strings being byte/ASCII arrays while several languages, Elixir and Rust included, immediately tell you that their strings are a list of UTF-8 characters (graphemes and codepoints can be extracted separately as well which is very useful).