四分律行事鈔資持記 1.530

1.530

僧界中。令不出界者，自然不攝法地人故。唱內相者，中留自然也。如下，舉例。如前釋。

In the monks' boundary: "Causing them not to leave the boundary" is because a natural boundary does not encompass the persons on the consecrated ground. "Chanting the inner markers" means leaving a natural boundary in the middle. From "such as..." onward, it adduces an example, as explained before.