Mail Merge Header Data Source

Source Relationship:

http://schemas.openxmlformats.org/officeDocument/2006/relationships/mailMergeHeaderSource

A document that stores information about a mail merge operation is permitted to contain a Document Settings part (§11.3.3) whose relationship item targets the file location of the necessary header data source using this relationship.

example:
<Relationships xmlns="…">
  <Relationship Id="rId2"
    Type="http://…/mailMergeHeaderSource"
    Target=http://www.openxmlformats.org/header.txt
    TargetMode="External"/>
</Relationships>

The document’s Document Settings part contains a <headerSource> element< >that explicitly references this relationship:

<w:settings …>
  <w:mailMerge>
    
    <w:headerSource r:id="rId2" /></w:mailMerge>
</w:settings>

A mail merge header data source shall be located external to the package containing the source relationship (expressed syntactically, the @TargetMode attribute of the <Relationship> element shall be External).