Presets: combo box syled element to setting the key to a fixed predefined value

[Fabi2]

To circumvent the bad parsing bahaviour of keys styled as:

key=value1;value2;value3;...

I let the user choose a fixed predefined values in the key in this proposal:

​http://wiki.openstreetmap.org/wiki/Proposed_features/Healthcare_2.0

Yes, this is now very common until now, but I don't want to see e.g. 10 values (or maybe more) as ​here in the value field, even when some people tried to convince me to use a key such as health_specialty=a;b;c;d;... as the next will enter the same as e.g. health_specialty=b;d;a;c;... and so on.

This is why the requested feature should made it possible to present a list of fixed predefined values as already possible with:

values="entry1,entry2,entry3"

and

display_values="Entry1,Entry2,Entry3"

but only for the value and not for the key.

The usage concept should be one of the following two cases:

1. It is only possible to select a value from a pre-defined list in the combo box, which is read only. The value of the key must then be a fixed value such as "yes". This single combo box will be presented to the user as it is still done.

2. It should optional possible to put a second combo box for the value beside the first one for the key. Which works as it already did. In this case the user should be forced to select a value from the combo box for the key first, if it is set to undefined. After he selected one of the pre-defined keys, the second value combo box will be actived, which is disabled otherwise..