Missing documentation

To whom it may concern: The PHP documentation nowhere indicates whether it's legal to *modify* a string by accessing an individual character in the string with the index operator (curly braces) and an assignment statement, as in: $str = '0123456789'; $str{4} = 'd'; // Now $str should be '0123d56789' While it does work on my machine, I feel the behavior should be documented, as * for all I know, there may be strange side effects (given php's complex copy semantics); * using undocumented language features can result in code that doesn't age or port well; * this is a fundamental aspect to any computer language. Sincerely, Stephen J. Fromm, PhD Bethesda, MD 20814