The word "之内" is formed through the direct combination of two characters: the classical grammatical particle "之", which here functions as a linking marker equivalent to "of", and the character "内", which means "inside" or "interior". Their fusion creates a single, fixed unit that expresses the spatial or abstract concept of "within the confines of" something, where the first character establishes a relational connection to a noun and the second character provides the core meaning of interiority.