Merge branch 'hotfix/#6891-#6778-composer-json-string-escaping'

Close #6891
Fix documentation typo
Remove inconsistent see tag
Reproducing test case for #6263 #6518
Workaround for #6263, which is related to #4482
Additional unit test to assert behavior of extract()
Refactor Collection::extract to reduce branch depth & add documentation
Merge branch 'hotfix/#6880-form-element-can-be-added-to-a-fieldset'

Close #6880
Close #6518
Close #6263
Merge branch 'hotfix/#6880-form-element-can-be-added-to-a-fieldset' into develop

Close #6880
Close #6518
Close #6263
Forward port #6880
Forward port #6518
Forward port #6263
Repeal `autocomplete` form attribute being boolean

`autocomplete` attribute may have string values:
http://www.whatwg.org/specs/web-apps/current-work/multipage/association-of-controls-and-forms.html#attr-fe-autocomplete
#6464 - assertions should fail if attribute is being prefixed by `data-`
#6464 - autocomplete is not a boolean value anymore
#6464 - autocomplete supports non-boolean values (behaves like a text attribute)
Merge branch 'hotfix/#6464-allow-non-boolean-autocomplete-attribute-values' into develop

Close #6464
Refactor german (de) Zend_Validate.php

- Corrected placeholder token '%' for some translations
- Add new class names
- Replace '' with ""
Remove dublicated "eingegeben"
Fix typos
Fix typos
Replace "Eingabewert" with "Eingabe"
Replace "String" with "Zeichenkette"