A few nits with the regex bits (these are common traps, even for experts):

• The regex metacharacter ^ means "start of string", not "start of line" (unless the /m modifier is used)
• The regex metacharacter $ means "end of string", not "end of line" (unless the /m modifier is used)
• . is "any char except \n" or just "not \n" (unless the /s modifier is used)

A few possible additions:

• Regex "start of string" is \A
• Regex "end of string" is \Z
• Regex "absolute end of string (i.e. no trailing \n) is \z
• Another commonly ignored "NEVER" is: /$userinput/