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Each header item is called a component and is composed of a keyword or
name, along with associated text. The keyword begins at the left margin,
-may NOT contain spaces or tabs, may not exceed 63 characters (as specified
+may
+.I not
+contain spaces or tabs, may not exceed 63 characters (as specified
by RFC 822), and is terminated by a colon (`:'). Certain components
(as identified by their keywords) must follow rigidly defined formats
in their text portions.