The headline averages families; tags only select tests
Headline
mean of the families' scores
Text
present, order,
repeat
Tables
table_cell
Layout
layout_kind
Test
one yes/no claim about one page
Arg
content at one place on the page
Tags
table, math, language, etc.
A test's tags are the union of its args' tags.
Tags select tests for any query; they never weigh the headline.