public float getPartialSpan(int p0,
    int p1)
Determines the span along the same axis as tab
expansion for a portion of the view.  This is
intended for use by the TabExpander for cases
where the tab expansion involves aligning the
portion of text that doesn't have whitespace
relative to the tab stop.  There is therefore
an assumption that the range given does not
contain tabs.

 public float getTabbedSpan(float x,
    TabExpander e)
Determines the desired span when using the given
tab expansion implementation.  If a container
calls this method, it will do so prior to the
normal layout which would call getPreferredSpan.
A view implementing this should give the same
result in any subsequent calls to getPreferredSpan
along the axis of tab expansion.