20.1.6 Isearch Yanking
The characters C-w and C-y can be used in incremental
search to grab text from the buffer into the search string. This
makes it convenient to search for another occurrence of text at point.
C-w copies the character or word after point as part of the
search string, advancing point over it. (The decision, whether to
copy a character or a word, is heuristic.) Another C-s to
repeat the search will then search for a string including that
character or word.
C-y is similar to C-w but copies all the rest of the
current line into the search string. If point is already at the end
of a line, it grabs the entire next line. Both C-y and
C-w convert the text they copy to lower case if the search is
currently not case-sensitive; this is so the search remains
case-insensitive.
C-M-w and C-M-y modify the search string by only one
character at a time: C-M-w deletes the last character from the
search string and C-M-y copies the character after point to the
end of the search string. An alternative method to add the character
after point into the search string is to enter the minibuffer by
M-e and to type C-f at the end of the search string in the
minibuffer.
The character M-y copies text from the kill ring into the search
string. It uses the same text that C-y as a command would yank.
Mouse-2 in the echo area does the same.
See Yanking.