What it reads. registry.pol files (the PReg format Group Policy stores under Machine and User); a GPO backup folder or a ZIP of one (Backup-GPO output, read from DomainSysvol\GPO\Machine|User\registry.pol, with the GPO's name from bkupInfo.xml); SYSVOL policy folders; and gpreport.xml from Get-GPOReport -ReportType Xml, whose Administrative Templates policies are matched by name and category and whose extra registry settings by value. A loose registry.pol is read as computer or user configuration as you choose; in a folder its Machine or User folder says which.
How it matches. Each registry value is looked up among the registry values the chosen products' latest templates write, and among settings their retained releases removed or renamed. A value no setting names counts toward a list only where one setting writes a list under that key. “Changed” means a substantive change (registry values, options, limits, choices, scope, category or supported platforms) in a retained release; wording-only changes are left out. History starts with the oldest release this installation keeps, so a change before it is not known here.
Limits. Up to 16 MB per registry.pol, 32 MB per report, 128 MB per ZIP (ZIP64 and encrypted archives are not read; extract them and choose the folder), and 5,000 files per folder. Report policy names are matched in English. A template describes what a setting writes, not whether it applies on your devices.