TAG_idx
is the position where (for
any abstract grammar tree) the tag of the tree resides. So, given any grammar
tree, t, then t[TAG_idx]
is a number that identifies the particular
kind of tree we are dealing with. The result is a number that can be tested to
be equal to NBR_tag
,FRC_tag
,TXT_tag
, TAB_tag
,
FUN_tag
,NAT_tag
,VAR_tag
, APL_tag
,
TBL_tag
, DEF_tag
,SET_tag
,DCT_tag
or VOI_tag
.