How Does PO Approval Button Call the PO Approval Workflow

How does the Enter Purchase Order or the Enter Requisition screen Approve button call the Purchasing approval workflow?

When the Approve button is clicked, the approval modal window form for purchasing approvals iscalled (this is form POXDOAPP.fmb and its attached corresponding library file POXAPAPC.pll.).

Both Enter Requisition and Enter Purchase Order forms call the the same approval form.

The library file POXAPAPC.pll has a procedure PO_WF_APPROVE_C.SetUpWorkFlow that calls the procedure PO_REQAPPROVAL_INIT1.Start_WF_Process in package file POXWPA1B.pls. This server side procedure calls the workflow and initiates the workflow and processes the document through the workflow using these parameters:

PO_REQAPPROVAL_INIT1.Start_WF_Process ( ItemType => ItemType,
ItemKey => ItemKey,
WorkflowProcess => WorkflowProcess,
ActionOriginatedFrom => ActionOriginatedFrom,
DocumentID => DocumentID,
DocumentNumber => DocumentNumber,
PreparerID => PreparerID,
DocumentTypeCode => DocumentTypeCode,
DocumentSubtype => DocumentSubtype,
SubmitterAction => RequestorAction,
forwardToID => forwardToID,
forwardFromID => forwardFromID,
DefaultApprovalPathID => DefaultApprovalPathID,
Note => DocumentNote,
printFlag => print_check,
FaxFlag => fax_check,
FaxNumber => fax_number,
EmailFlag => email_check,
EmailAddress =>; emailaddress,
CreateSourcingRule => Create_Sourcing_Rule,
UpdateSourcingRule => Update_Sourcing_Rule,
ReleaseGenMethod =>; Rel_Gen_Mthd,
MassUpdateReleases => l_massupdate_release, — RETROACTIVE FPI CHANGE
RetroactivePriceChange => ‘N’ , — RETROACTIVE FPI CHANGE
OrgAssignChange => l_org_assign_change );