This bug has been fixed in the documentation's XML sources. Since the
online and downloadable versions of the documentation need some time
to get updated, we would like to ask you to be a bit patient.

Thank you for the report, and for helping us make our documentation better.

The change does not address the issue. Changing the `"$a[a]"` to `"$a['a']"` only 
serves to break the example (literally, it will generate a parse error).

The point, I think, was that the reporter (mistakenly) did not like the idea of 
using a "bad practice".  However, "$a[a]" is perfectly acceptable (within a 
string!) and will not generate any notices.  

The description could do with mentioning that T_STRING also means 
class/function/etc. names as well.

salathe is perfectly right (in all points). I didn't realize, that "$a[a]" is valid within a string. (Actually I had my thoughts on the complex variable syntax "{$a[a]}" there it *would* be a notice.) I am sorry for that. But the point about not mentioning identifiers like class and function name is still valid.

<row>
    <entry><constant>T_STRING</constant></entry>
    <entry>"$a[a]", identifier</entry>
    <entry>string array index inside string or identifier, e.g. function or class name</entry>
</row>

Better turn it round or it is ambiguous (array index inside identifier one could think):

<row>
    <entry><constant>T_STRING</constant></entry>
    <entry>identifier, "$a[a]"</entry>
    <entry>identifier ( e.g. function or class name) or string array index inside string</entry>
</row>

See also #52927 referencing the misinformation from the committed "fix" for this 
bug.

I'm sorry for the duplicate (#52927). I've tested the original syntax "$a[b]" and it reports b as a T_STRING token. If I understand this correctly within strings it's permitted to use identifiers as string indices to avoid complex escaping. However outside of a string it's (rightfully) considered bad style.

If this is correct T_STRING is ALWAYS an identifier and "$a[b]" is just a special case where it's ok to use an identifier as a string index.

This bug has been fixed in the documentation's XML sources. Since the
online and downloadable versions of the documentation need some time
to get updated, we would like to ask you to be a bit patient.

Thank you for the report, and for helping us make our documentation better.