Percent Overlap in WO Routing

Hello,

I read several documents mentioning Percent Overlap, each one stating what it is used for and none explaining how it really affects WO processing. Can someone please answer the following two questions:

Scenario:

The Routing has two operation, with the Percent Overlap setup that allows second operation to begin when the first one is 80% complete.

Questions:

1) What criteria does the system use to determine that the first operation is 80% complete (e.g. 80% of material issued for that operation, or 80% of hours backflushed for that operation, or ...)?

2) Does the system generate warning or error on an attempt to begin second operation by issuing material or backflushing hours when the first one is not yet 80% complete?