WV is used to attach the wall to the head-verb of the sentence. The goal of WV is to make the correspondance between link-grammar and traditional dependency grammars more concrete. WV always makes a cycle with the W link, which identifies the subject.
+------WV------+
+---Wd---+-Ss*b+
| | |
LEFT-WALL this is an example
WV attaches to the head, rather than to any auxiliary verbs:
+----------WV----------+
+---Wd---+-Ss*b-+--Ix--+
| | | |
LEFT-WALL this could be an example
+---------WV---------+-----IV----+
+---Wd---+-Ss*b+-Pgfb+--TOf-+-Ix-+
| | | | | |
LEFT-WALL this is going to be an example
See also the CV link, for connecting to head-verbs of clauses, the IV link for connecting to the head-verb of infinitive clauses and the AF link for connecting to adjectival complements. Sometimes, the B link can play a similar role for relative clauses (and the R link being analogous to the W link):
+---------Bs---------+
+-Rn-+-Sp*i+----PP---+
| | | |
the dog I had chased was black
See also the CP link, which connects to quotation and paraphrasing verbs, as does Eq link and COq link.