Special properties (declarative)

This help page lists the declarative special properties. Declarative special properties are used to define or declare the behaviour of properties on their properties pages, i.e. they can only be used in namespace "Property". Starting with Semantic MediaWiki 3.0.0Released on 11 October 2018 and compatible with MW 1.27.0 - 1.31.x. error messages1 will be issued if a declarative special property is used in other namespaces than that.2

The following table gives an overview of all 18 visible special properties provided by Semantic MediaWiki:

Name	Description	Help page	Since	Key
Allows value	Lists one permissible value for a property	Special property "Allows value"	1.0	_PVAL
Corresponds to	Gives the conversion factor for some unit of a physical quantity and the possible names for that unit	Special property "Corresponds to"	1.0	_CONV
Display units	Specifies the a comma-separated list of units or formats that a property should use in display	Special property "Display units"	1.0	_UNIT
Equivalent URI	Marks a page in the wiki as having a well-known meaning beyond this wiki, in an external URI	Special property "Equivalent URI"	1.0	_URI
Has type	Assigns a datatype to a property	Special property "Has type"	1.0	_TYPE
Imported from	Allows users to reuse elements of external vocabularies directly within the wiki	Special property "Imported from"	1.0	_IMPO
Provides service	Adds service links to properties	Special property "Provides service"	1.0	_SERV
Subproperty of	Lets you indicate that one property is a subproperty of another	Special property "Subproperty of"	1.0	_SUBP
Has fields	Defines a short list of fields with a fixed type and order for datatype Record	Special property "Has fields"	1.5.0	_LIST
Subcategory of	Lets you explicitly indicate that one category is a subcategory of another	Special property "Subcategory of"	1.5.0	_SUBC
Allows pattern	Pattern to match a permissible value	Special property "Allows pattern"	2.4.0	_PVAP
Display precision of	Allows to define the display precision in digits	Special property "Display precision of"	2.4.0	_PREC
Has property description	Adds localizable context help to properties	Special property "Has property description"	2.4.0	_PDESC
Has uniqueness constraint	Allows to restrict value annotation to be unique	Special property "Has uniqueness constraint"	2.4.0	_PVUC
Allows value list	Adds a reference to a list of permissible values for a property	Special property "Allows value list"	2.5.0	_PVALI
External formatter URI	Declares an external URL with placeholders $1, $2	Special property "External formatter URI"	2.5.0	_PEFU
Has preferred property label	Adds localizable labels to a property	Special property "Has preferred property label"	2.5.0	_PPLB
Change propagation	Holds the new property specification of a property or category page	Special property "Change propagation"	3.0.0	_CHGPRO

Conversely all special properties not listed here are not declarative.

Special property "Subcategory of"Lets you explicitly indicate that one category is a subcategory of another and special property "Change propagation"Holds the new property specification of a property or category page can also be used in namespace "Category".