Answer
Yes — a set of predefined session/context values can be used directly inside Text-type field expressions, each written wrapped in # marks: #USER_DIRECTORY_ID# (the logged-in user's Directory ID, in <Domain>\<Username> or <Username> form), #USER_EMAIL# (their email address), #USER_ID# (their user ID), #USER_LANGUAGE# (their current language), #DEFAULT_COMPANY# (the standard/default company), #PERSON_ID# (the person's identification), and #PERSON_NAME# (the person's name). These values are also offered directly in the field's search-help/autocomplete picker, so they don't need to be memorized exactly — clicking to select one from that list inserts the correctly-spelled token automatically.