.RELS File Extension
File TypeOpen Office XML Relationships File
What is a RELS file?
A RELS file is a metadata file contained within Microsoft Open Office XML documents. It stores XML specifications for how "parts" within a "package" are connected to form a document. RELS files are saved in a _rels directory of an Open Office XML document.
RELS files are not meant to be opened manually. Instead, the file is referenced by the Microsoft Office application opening the document that contains the RELS file.
You can view the contents in a RELS file with a text editor since the information is saved in XML format. However, you should not edit the contents it may cause the document that contains the RELS file to become unusable.
Relationships within RELS files are declared using the XML syntax <Relationship Id="someID" Type="relationshipType" Target="targetPart"/>, where Id is the unique user-defined string, Type is the type of content, and Target is the target file used for the relationship.