<the literal < (6010 / 748 / 3C16)
\s*any whitespace character, repeated any number of times
\/?optionally matches the literal / (4710 / 578 / 2F16)
\s*any whitespace character, repeated any number of times
imgthe literal text img (case sensitive) Negative Lookahead(?![^>]*class=) Negated Character Class[^>]* *matches any number of characters outside the set below:
>the literal > (6210 / 768 / 3E16)
class=the literal text class= (case sensitive) g modifier: global. Finds all matches instead of stopping after the first