#### Description:

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.

Type:

  Integer.

#### Applicability

##### FrameSet

All FrameSets have this attribute.

#### Notes:

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

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