XmTabSetValue sets the value field of the XmTab structure associated with tab.
tab Specifies the tab to set the value of.
value Specifies the floating point number which represents the distance that the rendering of the
XmString segment associated with tab will be offset. The offset is from either the beginning of
the rendering or from the previous tab stop, depending on the setting for the offset model. The
distance depends on the tab's unit type. Note that negative values are not permitted, and that
if a tab stop would cause text to overlap, the x position for the segment is set immediately
after the end of the previous segment.