You're not just being a rigid boundary person.

Again, these dates are meant as a tool to help understand the types of procedure in use, not as a rigid boundary where one system stopped and another began.

Lustre varies over a wide continuum, and so there are no rigid boundaries between the different types of lustre.

Her proteiform body of work lies on a contrasted dialog between the ever-changing psychological identity and the rigid boundaries of physical identification.

These commonly used descriptive terms do not necessarily use the official or current names for features; and often these concepts of places don't have clear, rigid boundaries.