This code system http://hl7.org/fhir/concept-property-type defines the following codes:

CodeDisplayDefinition
code code (internal reference)The property value is a code that identifies a concept defined in the code system.
Coding Coding (external reference)The property value is a code defined in an external code system. This may be used for translations, but is not the intent.
string stringThe property value is a string.
integer integerThe property value is an integer (often used to assign ranking values to concepts for supporting score assessments).
boolean booleanThe property value is a boolean true | false.
dateTime dateTimeThe property is a date or a date + time.
decimal decimalThe property value is a decimal number.
<status value="active"/><experimental value="false"/><date value="2021-01-05T10:01:24+11:00"/><publisher value="HL7 (FHIR Project)"/><contact><telecom><system value="url"/><value value="http://hl7.org/fhir"/></telecom><telecom><system value="email"/><value value="fhir@lists.hl7.org"/></telecom></contact><description value="The type of a property value."/><jurisdiction><coding><system value="http://unstats.un.org/unsd/methods/m49/m49.htm"/><code value="001"/><display value="World"/></coding></jurisdiction><caseSensitive value="true"/><valueSet value="http://hl7.org/fhir/ValueSet/concept-property-type"/><content value="complete"/><concept><code value="code"/><display value="code (internal reference)"/><definition value="The property value is a code that identifies a concept defined in the code system."/></concept><concept><code value="Coding"/><display value="Coding (external reference)"/><definition value="The property value is a code defined in an external code system. This may be used for translations, but is not the intent."/></concept><concept><code value="string"/><display value="string"/><definition value="The property value is a string."/></concept><concept><code value="integer"/><display value="integer"/><definition value="The property value is an integer (often used to assign ranking values to concepts for supporting score assessments)."/></concept><concept><code value="boolean"/><display value="boolean"/><definition value="The property value is a boolean true | false."/></concept><concept><code value="dateTime"/><display value="dateTime"/><definition value="The property is a date or a date + time."/></concept><concept><code value="decimal"/><display value="decimal"/><definition value="The property value is a decimal number."/></concept></CodeSystem>