modelineexpr

modelineexpr is a term that refers to an expression used within Emacs modelines to define how information is displayed. Emacs modelines are the status lines at the bottom of each window, typically showing information about the buffer, its mode, and other relevant details. The modelineexpr allows for highly customizable display of this information.

These expressions are written in the Emacs Lisp programming language. They are evaluated by Emacs and their return value is then rendered in the modeline. This provides a powerful mechanism for users to tailor the modeline to their specific needs and preferences, displaying anything from buffer name and major/minor modes to version control status, line and column numbers, and even custom project-specific information.

The structure of a modelineexpr can range from simple variables to complex Lisp functions that dynamically fetch and format data. Developers and advanced users often create sophisticated modelineexprs to display a wealth of contextual information that enhances productivity and provides immediate feedback on the state of their work within Emacs. The flexibility offered by modelineexprs is a key reason for Emacs's reputation as a highly extensible and personalizable editor.