33.8.3 Yanking

Yanking means inserting text from the kill ring, but it does not insert the text blindly. The yank command, and related commands, use insert-for-yank to perform special processing on the text before it is inserted.

Function: insert-for-yank string ¶

This function works like insert, except that it processes the text in string according to the yank-handler text property, as well as the variables yank-handled-properties and yank-excluded-properties (see below), before inserting the result into the current buffer.

string will be run through yank-transform-functions (see below) before inserting.

Function: insert-buffer-substring-as-yank buf &optional start end ¶

This function resembles insert-buffer-substring, except that it processes the text according to yank-handled-properties and yank-excluded-properties. (It does not handle the yank-handler property, which does not normally occur in buffer text anyway.)

If you put a yank-handler text property on all or part of a string, that alters how insert-for-yank inserts the string. If different parts of the string have different yank-handler values (comparison being done with eq), each substring is handled separately. The property value must be a list of one to four elements, with the following format (where elements after the first may be omitted):

(function param noexclude undo)

Here is what the elements do:

function

When function is non-nil, it is called instead of insert to insert the string, with one argument—the string to insert.

param

If param is present and non-nil, it replaces string (or the substring of string being processed) as the object passed to function (or insert). For example, if function is yank-rectangle, param should be a list of strings to insert as a rectangle.

noexclude

If noexclude is present and non-nil, that disables the normal action of yank-handled-properties and yank-excluded-properties on the inserted string.

undo

If undo is present and non-nil, it is a function that will be called by yank-pop to undo the insertion of the current object. It is called with two arguments, the start and end of the current region. function can set yank-undo-function to override the undo value.

User Option: yank-handled-properties ¶

This variable specifies special text property handling conditions for yanked text. It takes effect after the text has been inserted (either normally, or via the yank-handler property), and prior to yank-excluded-properties taking effect.

The value should be an alist of elements (prop . fun). Each alist element is handled in order. The inserted text is scanned for stretches of text having text properties eq to prop; for each such stretch, fun is called with three arguments: the value of the property, and the start and end positions of the text.

User Option: yank-excluded-properties ¶

The value of this variable is the list of properties to remove from inserted text. Its default value contains properties that might lead to annoying results, such as causing the text to respond to the mouse or specifying key bindings. It takes effect after yank-handled-properties.

Variable: yank-transform-functions ¶

This variable is a list of functions. Each function is called (in order) with the string to be yanked as the argument, and should return a (possibly transformed) string. This variable can be set globally, but can also be used to create new commands that are variations on yank. For instance, to create a command that works like yank, but cleans up whitespace before inserting, you could say something like:

(defun yank-with-clean-whitespace ()
  (interactive)
  (let ((yank-transform-functions
	 '(string-clean-whitespace)))
    (call-interactively #'yank)))