This attribute gives the index of the Frame which is to be regarded as the " base" Frame within a FrameSet. The default is the first Frame added to the FrameSet when it is created (this Frame always has an index of 1).

When setting a new value for this attribute, a string may be supplied instead of an integer index. In this case a search is made within the FrameSet for a Frame that has its Domain attribute value equal to the supplied string (the comparison is case-insensitive). If found, the Frame is made the base Frame. Otherwise an error is reported.

FrameSet

• Inverting a FrameSet (inverting the boolean sense of its Invert attribute, with the AST_INVERT routine for example) will interchange the values of its Base and Current attributes.