Learn English – Name of a three-item list of verbs in sequence

Just about every diff (comparison) system I've used has labelled these source and target respectively.

Note that this convention does privilege the file named first -- the source -- as the canonical, "normative", reference. For example, if file1 has a line file2 lacks, then tools following this convention will say the line has been deleted (to produce the target) rather than added (because a source isn't produced).

For the sake of having a reference, the Wikipedia article on data differencing uses the terms this way, which means they will probably be clear enough to your audience without a lot of introduction.

By the way, for a little bit of fun, the two files, collectively, can be called the "comparands" (viz "operands", "summands", etc).

A sentence requires a subject and a predicate. A predicate is a verb plus whatever other elements make up a verb phrase. In this case, the subject, clearly, is I, while the predicate is the verb describing the state or action of the subject. In this case, that is want, in a transitive capacity. Everything after that is the direct object of want, a noun in effect, which can be replaced by a pronoun. In other words, this sentence can be reduced to I want it. The verb phrase itself contains two additional verb phrases, but the verb that is serving the subject is want.