Insert STRING at point for the `yank' command.
This function is like `insert', except it honors the variables
`yank-handled-properties' and `yank-excluded-properties', and the
`yank-handler' text property.
Properties listed in `yank-handled-properties' are processed,
then those listed in `yank-excluded-properties' are discarded.
If STRING has a non-nil `yank-handler' property on its first
character, the normal insert behavior is altered. The value of
the `yank-handler' property must be a list of one to four
elements, of the form (FUNCTION PARAM NOEXCLUDE UNDO).
FUNCTION, if non-nil, should be a function of one argument, an
object to insert; it is called instead of `insert'.
PARAM, if present and non-nil, replaces STRING as the argument to
FUNCTION or `insert'; e.g. if FUNCTION is `yank-rectangle', PARAM
may be a list of strings to insert as a rectangle.
If NOEXCLUDE is present and non-nil, the normal removal of
`yank-excluded-properties' is not performed; instead FUNCTION is
responsible for the removal. This may be necessary if FUNCTION
adjusts point before or after inserting the object.
UNDO, if present and non-nil, should be a function to be called
by `yank-pop' to undo the insertion of the current object. It is
given two arguments, the start and end of the region. FUNCTION may set `yank-undo-function' to override UNDO.