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is_viewer - Function

	Package	display
	Module	viewer

Is the argument a viewer tool?

Synopsis
is_viewer(tool)

Description
This global function can be used to determine if the supplied argument is a viewer tool. If so it returns True, otherwise it returns False.

Arguments

tool		The variable that you wish to test
		Allowed:	Any glish variable
		Default:	no default

Returns
T or F, indicating if the argument is a viewer tool or not.

Example

      include 'viewer.g';
      if (is_viewer(dv)) {
        myviewer := dv;
      } else {
        myviewer := viewer();
      }

This example shows how you can use this function to determine if the default viewer (dv) is a viewer tool.