Die Präposition vor verlangt hier einen anderen Kasus als die Präposition mit.

Here verlangt means requires or governs in a grammatical sense. It does not mean that the preposition is emotionally demanding something. In grammar explanations, German often uses verlangen to say which case a word takes.

For example:

• mit verlangt den Dativ
• für verlangt den Akkusativ

Because the sentence is talking about those words as grammatical items. Präposition is a noun meaning preposition, and it is feminine, so the subject is:

• die Präposition vor
• die Präposition mit

This is similar to English saying the preposition before or the preposition with.