Allow for open enumerations

base_classes/NXobject.nxdl.xml

@@ -30,5 +30,170 @@
 		This is the base object of NeXus
 	</doc>
         <!--attribute name="name"><doc>name of instance</doc></attribute-->
-</definition>
+	<field name="identifierNAME" type="NX_CHAR" nameType="partial">
+		<doc>
+			An identifier for a (persistent) resource.
+
+			An identifier, provided by some authority, that has been assigned to the
+			real-world object described by this ``NXobject``. To be useful, the identifier
+			must not be reassigned to a different real-world object. It is typical for
+			there to be some mechanism to resolve an identifier, obtaining metadata
+			about the object. Identifiers for which some guarantees exist regarding
+			this resolution process are called persistent identifiers.
+			Persistent identifiers are also known as PIDs.
+		</doc>
+		<attribute name="type" type="NX_CHAR">
+			<doc>
+				The type of identifier used.
+
+				It is recommended to use the most specific type when describing the identifier.
+
+				For example, all IGSNs are DOIs and all DOIs are Handles; however, an IGSN should have type IGSN (and not DOI or Hdl).
+				Similarly, an ARK, Purl, ORCID and ROR identifiers should have their corresponding types and should not use the more generic URL identifier.
+			</doc>
+			<enumeration open="true">
+				<item value="ARK">
+					<doc>
+						Archival Resource Key.
+
+						An ARK is a Uniform Resource Identifier (URI) designed to support long-term access to a variety of information objects.
+
+						Syntax: https://NMA/ark:/NAAN/Name[Qualifier]. Brackets indicate optional elements.
+						Example: https://example.org/ark:/12345/abcde
+					</doc>
+				</item>
+				<item value="DOI">
+					<doc>
+						Digital Object Identifier.
+
+						A DOI is a unique alphanumeric string used to identify digital content. It consists of a prefix and a suffix, separated by a slash.
+
+						Syntax: 10.XXXX/XXXXXX
+						Example: 10.1107/S1600576714027575
+					</doc>
+				</item>
+				<item value="Hdl">
+					<doc>
+						A handle is a unique identifier that consists of a prefix indicating the naming authority and a suffix representing the local name 
+						of a resource, cts. 
+
+						A handle is a unique identifier used to facilitate the identification and management of digital objects. It is composed of a prefix that 
+						indicates the naming authority and a suffix that specifies the resource's local name. 
+
+						This refers specifically to an ID in the Handle system operated by the Corporation for National Research Initiatives (CNRI).
+
+						Syntax: prefix/identifier
+						Example: 123456789/abc123
+					</doc>
+				</item>
+				<item value="IGSN">
+					<doc>
+						International Generic Sample Number.
+
+						The IGSN is a unique identifier assigned to a specific sample or specimen in the context of scientific research.
 
+						Since 2021, IGSNs are issued by DataCite, meaning that there are now DataCite-issued DOIs for all IGSNs, 
+						including those historical IGSNs issued beforehand. Therefore, the syntax is the same as for DOIs.
+
+						Syntax: 10.XXXX/XXXXXX
+						Example: 10.1107/S1600576714027575
+					</doc>
+				</item>
+				<item value="ISNI">
+					<doc>
+						ISNI is an ISO standard to uniquely identify individuals and organizations involved in creative work, including pseudonyms
+						and other public personas.
+
+						An ISNI-ID is made up of 16 digits, the last character being a check character. The check character may be either a decimal digit
+						or the character “X”.
+
+						A URL can be generated from the ISNI ID by combining it with the prefix https://isni.org/isni/, resulting in
+						https://isni.org/isni/{ISNI-ID}.
+
+						Syntax: 16 base-10 digits stored without any spaces.
+						Example: 0000000121032683
+					</doc>
+				</item>
+				<item value="ISSN">
+					<doc>
+						International Standard Serial Number
+
+						An ISSN is an 8-digit unique identifier used to distinguish a serial publication, whether in print or electronic form.
+						The last character (a digit or 'X') serves as a check character, making the ISSN uniquely defined by its first seven digits.
+
+						Syntax: NNNN-NNNC, where N a decimal digit character (i.e., in the set {0,1,2,...,9}), and C is in {0,1,2,...,9,X}
+						Example: 1234-5678 or 1234-567X
+					</doc>
+				</item>
+				<item value="ISSN-L">
+					<doc>
+						Linking ISSN
+
+						The linking The ISSN, or ISSN-L, is a specific ISSN that groups the different media of the same serial publication.
+
+						Syntax: NNNN-NNNC, where N a decimal digit character (i.e., in the set {0,1,2,...,9}), and C is in {0,1,2,...,9,X}
+						Example: 1234-5678 or 1234-567X
+					</doc>
+				</item>
+				<item value="ORCID">
+					<doc>
+						Open Researcher and Contributor identifier.
+
+						ORCID provides a free and persistent identifier that uniquely distinguishes authors and contributors in scientific research.
+
+						Syntax: https://orcid.org/XXXX-XXXX-XXXX-XXXX
+						Example: https://orcid.org/0000-0002-1825-0097
+					</doc>
+				</item>
+				<item value="PURL">
+					<doc>
+						Persistent Uniform Resource Locator.
+
+						A Persistent Uniform Resource Locator (PURL) is a type of URL designed to provide a stable, long-term reference to a web 
+						resource by using a resolver to redirect users to the resource's current location, even if it moves over time.
+
+						A PURL has three parts: (1) a protocol, (2) a resolver address, and (3) a name.
+
+						Syntax: https://purl.org/foo/bar
+						Example: https://purl.org/dc/elements/1.1/title
+					</doc>
+				</item>
+				<item value="ROR">
+					<doc>
+						Research Organization Registry
+
+						A ROR ID is a globally unique identifier for research organizations, enabling unambiguous linking of institutions across systems.
+
+						Syntax: https://ror.org/{ROR-ID}
+						Example: https://ror.org/052gg0110
+					</doc>
+				</item>
+				<item value="URL">
+					<doc>
+						Uniform Resource Locator
+
+						Also known as web address, a URL is the address used to access a resource on the internet, 
+						specifying its location and the protocol to retrieve it.
+
+						Syntax: scheme://domain:port/path?query_string#fragment_id
+						Example: https://www.example.com/about
+					</doc>
+				</item>
+				<item value="URN">
+					<doc>
+						Uniform Resource Name
+
+						A URN is a unique, persistent identifier for a resource regardless of where it is stored.
+
+						It is recommended that identifiers with more specific type attribute (such as DOI or ISSN) values should not be stored as a URN,
+						even when this is valid. As an example, the URN doi:10.1107/S1600576714027575 is a valid URN-based representation for the DOI
+						10.1107/S1600576714027575, but it is recommended to use type="DOI" in this case.
+
+						Syntax: urn:&lt;namespace&gt;:&lt;namespace-specific-string&gt;. The leading urn: sequence is case-insensitive.
+						Example: urn:isbn:0000000000000
+					</doc>
+				</item>
+			</enumeration>
+		</attribute>
+	</field>
+</definition>

base_classes/NXsource.nxdl.xml

@@ -47,7 +47,7 @@
 	</field>
 	<field name="type">
 		<doc>type of radiation source (pick one from the enumerated list and spell exactly)</doc>
-		<enumeration>
+		<enumeration open="true">
 			<item value="Spallation Neutron Source" />
 			<item value="Pulsed Reactor Neutron Source" />
 			<item value="Reactor Neutron Source" />

dev_tools/docs/nxdl.py

@@ -512,10 +512,16 @@ def _print_enumeration(self, indent, ns, parent):
         if len(node_list) == 0:
             return ""
 
-        if len(node_list) == 1:
-            self._print(f"{indent}Obligatory value:", end="")
+        if parent.attrib.get("open", "false") == "true":
+            self._print(
+                f"{indent}This is an open enumeration. Any of these values is suggested:",
+                end="",
+            )
         else:
-            self._print(f"{indent}Any of these values:", end="")
+            if len(node_list) == 1:
+                self._print(f"{indent}Obligatory value:", end="")
+            else:
+                self._print(f"{indent}Any of these values:", end="")
 
         docs = OrderedDict()
         for item in node_list:

nxdl.xsd

@@ -1232,6 +1232,11 @@ https://stackoverflow.com/a/48980995/1046449 -->
 
 				(This data type is used internally in the NXDL schema 
 				to define elements and attributes to be used by users in NXDL specifications.)
+
+				Enumerations can be closed or open. A closed enumeration is one where the list of
+				values are the only ones allowed for a specification. An open enumeration is one 
+				where the list of values is incomplete and additional values other than those listed
+				are allowed.
 
 				::
 
@@ -1279,6 +1284,14 @@ https://stackoverflow.com/a/48980995/1046449 -->
 				</xs:complexType>
 			</xs:element>
 		</xs:sequence>
+		<xs:attribute name="open" use="optional" type="nx:NX_BOOLEAN" default="false" >
+			<xs:annotation>
+				<xs:documentation>
+					Is this an open enumeration?
+					An open enumeration allows additional values not listed.
+				</xs:documentation>
+			</xs:annotation>
+		</xs:attribute>
 	</xs:complexType>
 
 	<xs:complexType name="dimensionsType">