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Description

This command provides a Tcl interface to the X selection mechanism and implements the full selection functionality described in the X Inter-Client Communication Conventions Manual (ICCCM), except that it supports only the primary selection.

The first argument to selection determines the format of the rest of the arguments and the behavior of the command. The following forms are currently supported:

selection :clear window
If there is a selection anywhere on window's display, clear it so that no window owns the selection anymore. Returns an empty string.
selection :get ?type?
Retrieves the value of the primary selection and returns it as a result. Type specifies the form in which the selection is to be returned (the desired "target" for conversion, in ICCCM terminology), and should be an atom name such as STRING or FILE_NAME; see the Inter-Client Communication Conventions Manual for complete details. Type defaults to STRING. The selection :owner may choose to return the selection in any of several different representation formats, such as STRING, ATOM, INTEGER, etc. (this format is different than the selection type; see the ICCCM for all the confusing details). If the selection is returned in a non-string format, such as INTEGER or ATOM, the selection command converts it to string format as a collection of fields separated by spaces: atoms are converted to their textual names, and anything else is converted to hexadecimal integers.
selection :handle window command ?type? ?format?
Creates a handler for selection requests, such that command will be executed whenever the primary selection is owned by window and someone attempts to retrieve it in the form given by type (e.g. type is specified in the selection :get command). Type defaults to STRING. If command is an empty string then any existing handler for window and type is removed.

When the selection is requested and window is the selection :owner and type is the requested type, command will be executed as a Tcl command with two additional numbers appended to it (with space separators). The two additional numbers are offset and maxBytes: offset specifies a starting character position in the selection and maxBytes gives the maximum number of bytes to retrieve. The command should return a value consisting of at most maxBytes of the selection, starting at position offset. For very large selections (larger than maxBytes) the selection will be retrieved using several invocations of command with increasing offset values. If command returns a string whose length is less than maxBytes, the return value is assumed to include all of the remainder of the selection; if the length of command's result is equal to maxBytes then command will be invoked again, until it eventually returns a result shorter than maxBytes. The value of maxBytes will always be relatively large (thousands of bytes).

If command returns an error then the selection retrieval is rejected just as if the selection didn't exist at all.

The format argument specifies the representation that should be used to transmit the selection to the requester (the second column of Table 2 of the ICCCM), and defaults to STRING. If format is STRING, the selection is transmitted as 8-bit ASCII characters (i.e. just in the form returned by command). If format is ATOM, then the return value from command is divided into fields separated by white space; each field is converted to its atom value, and the 32-bit atom value is transmitted instead of the atom name. For any other format, the return value from command is divided into fields separated by white space and each field is converted to a 32-bit integer; an array of integers is transmitted to the selection requester.

The format argument is needed only for compatibility with selection requesters that don't use Tk. If the Tk toolkit is being used to retrieve the selection then the value is converted back to a string at the requesting end, so format is irrelevant. .RE

selection :own ?window? ?command?
If window is specified, then it becomes the new selection :owner and the command returns an empty string as result. The existing owner, if any, is notified that it has lost the selection. If command is specified, it is a Tcl script to execute when some other window claims ownership of the selection away from window. If neither window nor command is specified then the command returns the path name of the window in this application that owns the selection, or an empty string if no window in this application owns the selection.


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