This section describes some variables that hold regular expressions used for certain purposes in editing:
This is the regular expression describing line-beginnings that separate pages. The default value is
"^\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.
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-startalso.) The default value is
"[ \t\f]*$", which matches a line that consists entirely of spaces, tabs, and form feeds (after its left margin).
This is the regular expression for recognizing the beginning of a line that starts or separates paragraphs. The default value is
"\f\\|[ \t]*$", which matches a line containing only whitespace or starting with a form feed (after its left margin).
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-endconstructs the regexp. That is why you should always call the function
sentence-endto obtain the regexp to be used to recognize the end of a sentence.
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),