Description:
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Octal escape sequences in double quotes or backticks are not checked for overflow.

Test script:
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<?php
echo ord("\777"[0]) . PHP_EOL;
echo ord("\666"[0]) . PHP_EOL;
echo ord("\555"[0]) . PHP_EOL;

Expected result:
----------------
Some kind of error, because all of \777, \666, \555 sequences are invalid, their value is greater than 255.

Actual result:
--------------
255
182
109