Rulesets allow you to fine-tune DiffMerge to handle different types of files. This includes things such as character encodings, end of line conventions, and whitespace handling.
DiffMerge uses the Ruleset settings and the list of Rulesets defined in the Options Dialog to control how a set of files are loaded from disk and compared in a File Diff or Merge Window.
DiffMerge includes a Default Ruleset and a list of Custom Rulesets. The Default Ruleset is used when the use of Custom Rulesets is disabled or when none of the Custom Rulesets is appropriate.