Functions execute statements or print HTML. There are 3 kinds of Vortex functions: script functions written in the script; user functions, linked into Vortex and extensible by a C programmer; and builtin functions, also linked into Vortex. Functions are called by giving the name in a tag, possibly followed by arguments as attributes:
When the function ends, script execution resumes at the statement following the call.
main, which must be defined in all Vortex
scripts, is the default start function of the script: execution begins
with a call to it. (A different start function can alternatively be
given in the URL; see here.)