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Kate Part’s modelines – also called Kate document variables – are Kate Part’s implementation of document variables, similar to Emacs and vim modelines.

Document variables can be used to set Kate settings local to a file. This is for example for using another indenter than the one defined in the GUI settings. Or assume you work on two projects, the first indents with spaces and the second with tabs, then you can simply add a modeline that contains the specific document variables that set the specific indentation properties.