XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (449 page)

The name
quantified expression
comes from the mathematics on which these expressions are based: the
some
expression is known in formal logic as an existential quantifier, while the
every
expression is known as a universal quantifier.

As with the
for
expression, these two expressions bind a range variable to every item in a sequence in turn, and evaluate an expression (the
satisfies
expression) for each of these items. Instead of returning the results, however, a quanitified expression evaluates the effective boolean value of the
satisfies
expression. In the case of
some
, it returns
true
if at least one of these values is
true
, while in the case of
every
, it returns
true
if all of the values are
true
. The range variables can be referenced anywhere in the expression following the
satisfies
keyword, and the expression following the
in