Pressing C+b searches the current buffer and the current mode's keyword list for words beginning with the one before the caret.

This serves as a very basic code completion feature, for example:

- When editing any kind of program source, enter the first few characters of a previously-declared identifier name, invoke C+b, and save yourself from having to type it out again.
- When editing Javadoc comments in Java source code, enter "@" then press C+b to get a list of Javadoc tags.
- In a PHP file, enter a few characters and press C+b to see a list of functions whose names start with what you entered.