How to parse. ...

APPOSITION.

[Par. 138-140.

Here "the boy," being in close connection with
"Thomas," is said to be in Apposition (ad, near;
position, position) to " Thomas."
I38 For "the boy," write the Third Personal Pronoun. Then the sentence becomes(2) "Next came Thomas, he that cleans the boots."
(3) "Then we saw Thomas, him that cleans the
boots."
In (2) "Thomas" is the Subject, and the Pronoun in Apposition has the Subject-Inflection; in
(3) "Thomas " is the Object, and the Pronoun in
Apposition has the Object-Inflection. Hence we
get this Rule: -
Nouns and Pronouns are used Subjectively when
in Apposition to Subjects, and Objectively when in
Apposition to Objects.
I39 By " used Subjectively " or " Objectively" is meant that
-if the word has Subject and Object Inflections - the Subjective Inflection or Objective Inflection must be used.
I40 In most cases it may be shewn that words "used (1)
Subjectively " and (2) "Objectively" respectively, answer
the question (1) " who 2" or " what? " before the Verb, or
(2) "whom? " or " what?" after the Verb - so that they are
logical/l entitled to be described as being themselves Subjects
or Objects. Thus " he," above, answers " who came?"
Nouns or Pronouns in Apposition may be therefore described as Appositional Subjects or Objects
respectively.