Wrong syntax should be highlighted more explicitly

[koppor]

(Source for the syntax https://docs.jabref.org/finding-sorting-and-cleaning-entries/search#general-syntax)

We think, it is not an issue of the branch, but I want to report it.
It seems that JabRef sometimes shows the input field in red.

One has to move mouse to a certain position in JabRef

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old jabref marked the field red - to give "real" user feedback:

(I know, the red background was also used for something else)

[koppor]

Side track: (b|c)=2 is not handled intuitively with work in recent JabRef. Just works wiithout (). Syntax details: https://docs.jabref.org/finding-sorting-and-cleaning-entries/search#search-within-specific-fields