Hi Joachim,
Entity["PhysicalConstant"]["Properties"]
returns a list of EntityProperty that are formatted as light yellow boxes with the CommonName. CommonName can have spaces in them and are useful for using in textual descriptions.
Entity["PhysicalConstant"]["Properties"] // CommonName
(* {"abbreviation code", "alternate names", "ASCII description",
"classes", "conjectured value association", "conjectured values",
"description", "entity classes", "equal\[Hyphen]magnitude constants",
"equivalent forms", "external link", "Lévy\[Hyphen]Leblond class",
"name", "primary source", "quantity", "relative uncertainty", "series
expansion value association", "series expansion values", "standard
uncertainty", "standard year", "symbol", "value", "value
association", "values", "variants", "variant table"} *)
The CanonicalName needs to be used for accessing values.
Entity["PhysicalConstant"]["Properties"] // CanonicalName
(* {"AbbreviationCode", "AlternateNames", "ASCIIDescription", "Classes",
"ConjecturedValueAssociation", "ConjecturedValues", "Description",
"EntityClasses", "EqualMagnitudeConstants", "EquivalentForms",
"ExternalLink", "LevyLeblondClass", "Name", "PrimarySource",
"Quantity", "RelativeUncertainty", "SeriesExpansionValueAssociation",
"SeriesExpansionValues", "StandardUncertainty", "StandardYear",
"Symbol", "Value", "ValueAssociation", "Values", "Variants",
"VariantTable"} *)
Entity["PhysicalConstant"] // EntityList // CanonicalName
