SeverityNumber=0 MAY be used to represent an unspecified value

CHANGELOG.md

@@ -15,6 +15,9 @@ release.
 
 ### Logs
 
+- `SeverityNumber=0` MAY be used to represent an unspecified value.
+  ([#4535](https://github.com/open-telemetry/opentelemetry-specification/pull/4535))
+
 ### Baggage
 
 ### Resource

specification/logs/data-model.md

@@ -303,6 +303,8 @@ events. Larger numerical values in each range represent more important (more
 severe) events. For example `SeverityNumber=17` describes an error that is less
 critical than an error with `SeverityNumber=20`.
 
+`SeverityNumber=0` MAY be used to represent an unspecified value.
+
 #### Mapping of `SeverityNumber`
 
 Mappings from existing logging systems and formats (or **source format** for

specification/logs/supplementary-guidelines.md

@@ -198,7 +198,8 @@ type SeverityProcessor struct {
 // if the record's severity is greater than or equal to p.Min.
 // Otherwise, the record is dropped (the wrapped processor is not invoked).
 func (p *SeverityProcessor) OnEmit(ctx context.Context, record *sdklog.Record) error {
-	if record.Severity() != log.SeverityUndefined && record.Severity() < p.Min {
+	sev := record.Severity()
+	if sev >= log.SeverityTrace1 && sev <= log.SeverityFatal4 && sev < p.Min {
 		return nil
 	}
 	return p.Processor.OnEmit(ctx, record)
@@ -207,7 +208,7 @@ func (p *SeverityProcessor) OnEmit(ctx context.Context, record *sdklog.Record) e
 // Enabled returns false if the severity is lower than p.Min.
 func (p *SeverityProcessor) Enabled(ctx context.Context, param sdklog.EnabledParameters) bool {
 	sev := param.Severity
-	if sev != log.SeverityUndefined && sev < p.Min {
+	if sev >= log.SeverityTrace1 && sev <= log.SeverityFatal4 && sev < p.Min {
 		return false
 	}
 	if fp, ok := p.Processor.(sdklog.FilterProcessor); ok {