Custom properties enable users to define custom metadata properties through a set of well-defined data types.

Custom properties are represented by property elements (§7.3.2.2) stored in the Custom File Properties part with:

• Source Relationship: http://schemas.openxmlformats.org/officeDocument/2006/relationships/custom-properties

• Content Type: application/vnd.openxmlformats-officedocument.custom-properties+xml

Custom property elements are non-repeatable and may be empty or omitted. If all custom property elements are omitted then the custom properties part may be excluded from a document.

The type and value of custom properties are specified by child XML elements in the File Properties Variant Types namespace (discussed in detail in §7.4). User defined properties are uniquely identified through the name attribute of the property element. Custom properties can be associated with OLE document properties through the fmtid and pid attributes.

[Example: A custom OLE Editor property of type string can be defined as follows:

<property fmtid="{D5CDD505-2E9C-101B-9397-08002B2CF9AE}" pid="2"
name="Editor">
<vt:lpwstr>John Smith</vt:lpwstr>
</property>

end example]