Erubis is a fast, secure, and very extensible implementation of eRuby.
eRuby means "embedded Ruby" in documents.
Embedded patterns are '<% statement %>' and '<%= expression %>'.
The following is an example of eRuby. '<% ... %>' means Ruby statement
and '<%= ... %>' means Ruby expression. 

WWW: http://www.kuwata-lab.com/erubis/