if( 
    m[
        ^'?[a-z]                      ## start with letter or an apostrophy followed by one
        [a-z0-9'-_]+                  ## Alphanumeric + '-_
        (?[a-z0-9] | s') $            ## ends with alphanumeric or 
    ]x
    and not
    m[''|--]
}{
    ## Ok!
}