quote YAML strings starting with % or @ characters

Pygment uses the YAML 1.1 standard to parse YAML code being highlighted.
A string value cannot start with the percent sign or the @ character
in YAML 1.1 without being quoted. To highlight the YAML code blocks
properly, strings starting with the percent sign are now enclosed in
double quotes.
remove "..." from XML element tags

The ellipses were used as placeholders in XML element tags. Thus, the
XML wasn't well-formed and therefore would have never been rendered
properly.
link to the deployment index
apply headline guidelines to the cookbook articles
Added editorconfig
Fixed a minor syntax error
Also apply it for .rst.inc files
fix parent form types

The parent type of both the email type and the textarea type is not
the form type but instead the text type.
Update internals.rst

The proper idiom is "behind the scenes".

I also fixed the sentence structure.
minor #4034 Update internals.rst (redstar504)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #4034).

Discussion
----------

Update internals.rst

The proper idiom is "behind the scenes".

I also fixed the sentence structure.

Commits
-------

9966b90 Update internals.rst
Update page_creation.rst

Fix sentence structure.
Update page_creation.rst
minor #4036 Update page_creation.rst (redstar504)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #4036).

Discussion
----------

Update page_creation.rst

Fix sentence structure.

Commits
-------

7dafe20 Update page_creation.rst
85a3634 Update page_creation.rst
Update form_events.rst

EventSubscriberInterface::getSubscribedEvents() method is static.
Update form_events.rst

Remove extraneous quote.
bug #4031 Update form_events.rst (redstar504)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #4031).

Discussion
----------

Update form_events.rst

EventSubscriberInterface::getSubscribedEvents() method is static.

Commits
-------

a716a28 Update form_events.rst
229cde3 Update form_events.rst
Update submit.rst

Actually Rendered as ``button`` ``submit`` tag (not ``input`` ``submit``)
removed one space

removed one space
minor #4038 Update rendered tag (kirill-oficerov)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #4038).

Discussion
----------

Update rendered tag

Actually Rendered as ``button`` ``submit`` tag (not ``input`` ``submit``)

Commits
-------

1d50ce5 removed one space
067a447 Update submit.rst
minor #4030 enclose YAML strings containing % with quotes (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
----------

enclose YAML strings containing % with quotes

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #1886, #4029

Thanks @iamdto, did you spot some other occurences in the docs?

Commits
-------

c1c4bc8 remove "..." from XML element tags
dbc02a2 quote YAML strings starting with % or @ characters