The preceding sections merely introduce a subset of the constructs available in constructing procedure definitions. Additional facilities are provided for different kinds of loops, and for transferring control between procedure activations (e.g. using exitto). Moreover the Pop-11 "process" mechanism adds additional facilities not found in many languages.
Further reading can be found in later chapters, and in the following online help files
HELP CONTROL
HELP LOOPS
HELP PROCESS
REF SYNTAX
REF POPSYNTAX