For example, the Planck density, or Planck scale, is the density of matter above which the structure, and perhaps meaning, of space and time break down due to quantum mechanical effects.
(the Planck density, or Planck scale; is; the density of matter) (the structure, and perhaps meaning, of space and time; break down; due to quantum mechanical effects)
the Planck density, or Planck scale the structure, and perhaps meaning, of space and time
is break down
the density of matter
due to quantum mechanical effects