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34.8 Standard Regular Expressions Used in Editing

This section describes some variables that hold regular expressions used for certain purposes in editing:

user option page-delimiter

This is the regular expression describing line-beginnings that separate pages. The default value is "^\014" (i.e., "^^L" or "^\C-l"); this matches a line that starts with a formfeed character.

The following two regular expressions should not assume the match always starts at the beginning of a line; they should not use ‘^’ to anchor the match. Most often, the paragraph commands do check for a match only at the beginning of a line, which means that ‘^’ would be superfluous. When there is a nonzero left margin, they accept matches that start after the left margin. In that case, a ‘^’ would be incorrect. However, a ‘^’ is harmless in modes where a left margin is never used.

user option paragraph-separate

This is the regular expression for recognizing the beginning of a line that separates paragraphs. (If you change this, you may have to change paragraph-start also.) The default value is "[ \t\f]*$", which matches a line that consists entirely of spaces, tabs, and form feeds (after its left margin).

user option paragraph-start

This is the regular expression for recognizing the beginning of a line that starts or separates paragraphs. The default value is "\f\\|[ \t]*$", which matches a line containing only whitespace or starting with a form feed (after its left margin).

user option sentence-end

If non-nil, the value should be a regular expression describing the end of a sentence, including the whitespace following the sentence. (All paragraph boundaries also end sentences, regardless.)

If the value is nil, as it is by default, then the function sentence-end constructs the regexp. That is why you should always call the function sentence-end to obtain the regexp to be used to recognize the end of a sentence.

function sentence-end

This function returns the value of the variable sentence-end, if non-nil. Otherwise it returns a default value based on the values of the variables sentence-end-double-space (see Definition of sentence-end-double-space), sentence-end-without-period, and sentence-end-without-space.