Regex usage question

Hi All. Nice work on Pharo! We are starting to use the Regex pattern matching by allowing users to write "rules" using patterns. For example, our data lookup processing can include a 'Per' rule that takes a key such as 'xPerY' and returns the value of (data at: #x) / (data at: #y). Until recently, all binary-operators such as Per were performed with a simple string matches. But in order to generalize, we are moving regex patterns. Can someone tell me where the language-spec is for Regex-Core that is included in Pharo? Is this in the style of sed, awk, or ... ? If possible, how do I indicated that I want several sub-string replacement sections? Thanks in advance. -Cam