Complex sentence: The dominant in the tonicizing progression is referred to as a secondary dominant or V/x, V of x, where x is the tonicized scale degree, and may be replaced with a vii o chord.
Split into simpler sentences: The dominant in the tonicizing progression is referred to as a secondary dominant or V/x, V of x, where x is the tonicized scale degree. The V may be replaced with a vii o chord.