Description:
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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 of any computer language.