Sometimes one needs to do a search that involves a pattern, rather than
a fixed string. We call a string a pattern if it describes (in a special
language) a whole class of strings that could result in a successful
search. The language for such patterns is given in the next chapter on
regular expressions. It may also be needed sometimes to search
for strings that contain an end of line. If such a string is taken out
it would result in putting together two lines. Also this kind of
searches should be dealt with via the language of regular expressions.
Finally the regular expressions should also be used when the replacement
string contains an end of line, unless the user likes to see this end of
line inserted in the text as a funny character (sometimes needed in a
binary file).