NAME

selection − Manipulate the X selection

SYNOPSIS

selection get ?type?  selection handle window command ?type? ?format? 

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 selection get form of the command 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. 

The selection handle command creates a handler for selection requests: it arranges for command to 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. 

When the retrieval occurs, two additional numbers will be appended to command (with space separators), and the resulting string will be executed as a Tcl command.  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). 

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. 

If no handler has been declared for type TARGETS or type TIMESTAMP, Tk will automatically respond to selection requests for these types. 
 

KEYWORDS

format, handler, ICCCM, selection, target, type

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