"post_data = {'save[line[]]':'A line with text'}“


do you mean post_data = {'save[line][]':'A line with text'} ?
                                    ^^
is this you intention? 
array(
   'save' => 
        ['line' => 
             ['A line with text', 'maybe more lines']
        ]
); ?

Thank you for your reaction!
But no: I did in fact mean what I wrote. I realise it's a strange data structure, so here's a short explanation for it: the 'save' array holds a collection of html form elements that are not yet to be submitted, but should be saved temporarily into some other set of memory, so that upon the next visit, those temporary values can be easily inserted into the displayed form, without having been submitted. In other words, it's for a form that remembers its state throughout visits. 

So I send an object containing the name-value pairs in the form, and send that over POST. In the example used here, this results in one or more name-value pairs that are saved into the save array, as save['line[]'] = value. 

And that is the situation that triggers this bug, as in my original post. I'm sure there are other ways to achieve what I want, but I figured I'd report it since this does not look as if it's intended. 

Note that the example is a simplification of my application, where multiple 'single' and 'array' values are saved.

PHP won't allow variables name to contains "[", "." etc , so I think this is 
really a narrow usage.

but, however I do believe there is a bug.

a patch will be attached. but I need to ask someone else's opinion before commit 
it.

thanks

The attached patch may break form like: foo[bar][index]=test

after some research, this seems a undocumented behavior but not a bug.

only the field name `save` can not have '[' and other special chars.
the subkeys didn't required to be a legal variable name but '[]' are special
chars.

I noticed, that's why I didn't going further, 

and I don't think it related to documented or not:
<?php

$array ["[]"] = "xxxx";
var_dump($array["[]"]);

No feedback was provided. The bug is being suspended because
we assume that you are no longer experiencing the problem.
If this is not the case and you are able to provide the
information that was requested earlier, please do so and
change the status of the bug back to "Re-Opened". Thank you.

So far I've actually circumvented the bug (or feature), but that makes my code look a bit weird as I'm accessing data like $arr["somkey["]. 

Here's a short case that shows exactly what happens: 

$str = "arr[weirdkey[]]=foo&arr[otherkey[]]=bar";
parse_str($str, $output);
var_dump($output);

I'll probably end up changing how my application works, but still, I feel like something is amiss in how it currently works. I feel like it should either keep track of the brackets and so use -everything- inside the outer brackets as the key for the array; or otherwise, if the parser simply stops at the first ] (which is fine), I feel like I should get a notice or warning or... something somewhere, since there's another ] before the =. It's like arr[key]]=foo, isn't that supposed to fail?