As we have seen above, clauses may be <wh>=+ or <wh>=-,
may have one of several complementizers or no complementizer, and can be of
various clause types. The XTAG analysis uses three features to capture these
possibilities: <comp> for the variation in complementizers, <wh> for the question vs. non-question alternation and <mode>8.5 for clause types. In addition
to these three features, the <assign-comp> feature represents
complementizer requirements of the embedded verb. More detailed discussion of
the <assign-comp> feature appears below in the discussions of
sentential subjects and of infinitives. The four features and their possible
values are shown in Table 8.2.
