[colanderman]

Here's a good, valid, technical reason: any meta-programming tool – even a well-designed one – that strips out comments will now change the meaning of your code and silently fail.

If the annotation were instead, say, not inside the comments, then any such tool would either (a) leave the annotation intact, or (b) fail with an error when it encounters the unknown syntax.

[tomcorrigan]

Please provide an example of such a tool for PHP. Also provide a working example of PHP code where removing all annotations causes working code to fail silently. In my experience with using annotations in PHP if the annotations are missing/invalid the compiling code throws very descriptive error messages.

Your good, valid, technical reasons are anything but.