Defining a Rule
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The fromext represents the extension of a dependent file, and toext represents the extension of a target file.
.fromext.toext: commands
Extensions are not case sensitive. Macros can be invoked to represent fromext and toext; the macros are expanded during preprocessing. The period (.) preceding fromext must appear at the beginning of the line. The colon (:) is preceded by zero or more spaces or tabs. It can be followed only by spaces or tabs, a semicolon (;) to specify a command, a number sign (#) to specify a comment, or a newline character. No other spaces are allowed. Commands are specified as in description blocks.