As for me, though I have sometimes been critical of TA, and sometimes less than cautious in my words, my guesses at the two questions are: 1) There is no common underlying theory to all TA, there are
a variety of competing theories.
The opinions collected here» some dissenting from the majority
of the Court, others concurring in judgment but rejecting the majority's reasoning» show how Scalia applies his textualism to these issues, and how it differs from
competing theories of interpretation, most notably the «living Constitution» view favored by many on the left and the
varieties of intentionalism favored by many conservatives and moderates.