I'm learning German these days. I saw in a book that vor allem has the idiomatic meaning first of all. But to my confusion there is the example sentence
Die Leute liebten vor allen das gelbe Auto.
When should I use vor allem and when vor allen?
Later I saw in the grammar book :
For the pronoun
all, when it refers to things, it's regarded as neutral, singular (so ..em) and when it refers to people it is regarded as plural (so ..en). (when they are after preposition I guess)
Einige sind mit allem einverstanden. (Some people agree with everything)
Wir haben vorher mit allen diskutiert. (We have discussed it with everyone before)