If L is a regular language then also is the language $L1 = \{ w \in L | w \in L^R \}$?
The notation $L_1 = \{ w \in L \mid w \in L^R \}$ means "the collection of all $w \in L$ that satisfy the condition $w \in L^R$". In other words, $L_1 = L \cap L^R$.