[JieXiong9119]

Any background context you want to provide?

What does this PR do?

See proposal.

How should this be manually tested?

What are the relevant tickets?

Closes #297

Screenshots (if appropriate)

[JieXiong9119]

Note that this PR only adds the Type and applies it to one existing .../DerivedModelPerformance/CVRMSE element that has originally the inline 0-100 restriction. Other identified fields that should/could migrate to PercentType are listed below. It requires first resolving fraction-vs-percent values in examples and producer data (e.g. Audit Template) and is deferred to a major version as introducing breaking changes.

Candidate share-of-whole elements for a future (breaking) migration. Each is documented as a percentage of a bounded whole (area, floor area, length, time, consumption, savings), so values outside 0-100 are not meaningful. Example statistics are from all valid examples/*.xml; "Fractions" counts values strictly between 0 and 1.

Element	Current type	Target type	Uses in examples	Example range	Fractions	Fraction-to-percent fix needed?
PartialOperationPercentage	decimal + Source	PercentWithSourceAttribute	714	0 to 1	484	Yes: all values are fractions
PercentPremisesServed	decimal + Source	PercentWithSourceAttribute	38	0.05 to 1	6	Yes
PercentSkylightArea	decimal + Source	PercentWithSourceAttribute	50	0 to 0.0375	2	Yes
PercentResource	decimal	PercentType	13	1	0	Ambiguous: 1 probably means 100%
PercentEndUse	decimal	PercentType	13	1	0	Ambiguous: 1 probably means 100%
PipeLocation	decimal + Source	PercentWithSourceAttribute	4	1	0	Ambiguous
PercentOccupiedByOwner	decimal + Source	PercentWithSourceAttribute	6	20 to 78	0	No
PercentLeasedByOwner	decimal + Source	PercentWithSourceAttribute	6	15 to 80	0	No
SpatialUnitOccupiedPercentage	decimal	PercentType	1	90	0	No
PercentOfWindowAreaShaded	decimal + Source	PercentWithSourceAttribute	200	0	0	No
FloorAreaPercentage	float [0, 100]	PercentType	88	0 to 100	0	No; already bounded, change is float to decimal
PercentageOfCommonSpace	decimal + Source	PercentWithSourceAttribute	0	-	-	Not used in examples
BoilerPercentCondensateReturn	decimal + Source	PercentWithSourceAttribute	0	-	-	Not used in examples
DuctPressureTestLeakagePercentage	decimal + Source	PercentWithSourceAttribute	0	-	-	Not used in examples
SupplyDuctPercentConditionedSpace	decimal + Source	PercentWithSourceAttribute	0	-	-	Not used in examples
ReturnDuctPercentConditionedSpace	decimal + Source	PercentWithSourceAttribute	0	-	-	Not used in examples
DutyCycle	decimal + Source	PercentWithSourceAttribute	0	-	-	Not used in examples
PumpDutyCycle	decimal + Source	PercentWithSourceAttribute	0	-	-	Not used in examples
MinimumOutsideAirPercentage	decimal + Source	PercentWithSourceAttribute	0	-	-	Not used in examples
HumidityControlMinimum	decimal + Source	PercentWithSourceAttribute	0	-	-	Not used in examples
HumidityControlMaximum	decimal + Source	PercentWithSourceAttribute	0	-	-	Not used in examples
PercentGuaranteedSavings	decimal + Source	PercentWithSourceAttribute	0	-	-	Not used in examples
FederalSustainabilityChecklistCompletionPercentage	decimal + Source	PercentWithSourceAttribute	0	-	-	Not used in examples

Rates and ratios that can be negative or exceed 100 (EscalationRate and the price escalation rates, InflationRate, DiscountRate, DiscountFactor, InternalRateOfReturn, ProjectMarkup, DemandRatchetPercentage) are excluded.

No element names, paths, or enumerations change, so downstream repos (use-cases, BOSS, asset-extractor) are unaffected; bsyncpy gains two new types on regeneration.

[Copilot]

🟡 Changes recommended

The -100% lower bounds on NMBE and NDBE reject valid negative bias errors and need removal, along with corresponding range documentation updates.

1 open issue

• Remove overly restrictive -100% lower bounds for bias errors · New

What changed in this PR

This PR introduces reusable percentage types for BuildingSync, addressing part of #297 while deferring breaking changes to existing percentage fields.

Changes:

• Adds PercentType and a variant supporting the optional Source attribute.
• Reuses PercentType for CVRMSE without changing its accepted values.
• Widens NDBE and NMBE to accept values down to -100 and documents the non-breaking scope and future migration candidates.

File	Description
proposals/​2026/​Add PercentType and Allow Negative Bias Errors.md	Explains the rationale, compatibility classification, and deferred migrations.
BuildingSync.xsd	Defines percentage types, updates CVRMSE, and lowers bias-error bounds.

_{Review effort: Balanced}