The search buttons from the search form on the top of the page
as well as the search page both produce invalid HTML
due to the name attribute being empty.
As the name is required for each of the PHP functions
producing the buttons and is passed as an empty string,
this makes sure that parameters with empty strings get skipped.

This is useful for anonymously useable forms, like the search.

There was a bug, where the options array ['Auto', 0, 1] would result in
HTML option tags where both the 'Auto' and the 0 option were selected.

to 'OptGroup::options()' as this would lead to an <option> tag having two 'selected' attributes.

PHP 5.6 and below throw a strict standards warning at the changed lines.
An intermediate variable is introduced to avoid this warning.

PHP 7+ changes the severity of this warning to E_NOTICE which is
suppressed by DokuWiki.

This error was introduced in #1778

The problem this is solving is that PHP does not allow for array-keys to
be strings of ints. It always converts them to actual ints. This caused
a problem when trying to use complex array-options with integers as
keys.

We currently throw an exception with setting the multiple-attribute is
attempted. If we want to implement this functionality, it might be more
sensible to make an extra commit for that.

Multiple selected option would not be valid HTML.

In more complex selects we may want to group options by some criteria.
HTML has the <optgroup>-tag for that purpose.

However in Order to not duplicate code, I've to move the handling of
options to the OptGroup-Class completely.

Known Issues:
-------------
* We may have more than one option with the same value and therefore
more than one option may be marked as selected.

fixes #1776

Now classes and data- attributes can be added to individual options

Since Firebug it is no longer necessary to structure html with linebreaks. See also Issue #924

Textareas use CRLF, but internally we use LF.

when a form was submitted with an empty input, that data should still
overwrite the preset value.

Throwing an exception on request for an id or attribute breaks several
functions like $form->findPositionByAttribute.

See issue #1312

You now can add labels that don't wrap around inputs, but you have to
ensure IDs are properly assigned yourself.

The Label class has been renamed to LabelElement to reflect the naming
scheme of the other elements.

this is far from comprehensible, but should give an idea how the new
library works and how to write tests

This is jsut a small beginning. Not all elements are there, yet. It's
also completely untested so far.