zope.tales (Template Attribute Language - Expression Syntax) is an expression language designed to work with zope.tal (although it can be used independently). The two are integrated to produce page templates in zope.pagetemplate.
The specification for TAL and TALES can be found at https://pagetemplates.readthedocs.io/en/latest/
Documentation on this implementation and its API can be found at https://zopetales.readthedocs.io/