Metadata is typically stored in a separate file from the primary data, often in a structured format like XML or JSON. Common examples include ID3 tags in music files, EXIF data in images, and header information in documents like PDFs or Word files.

XRD stands for Extensible Resource Descriptor Sequence. It is a version of the XML format that allows users to discover various metadata aspects from documents being used.

You can find a list of frequently asked questions on the psol website about the topic XML/EDI. The edidev website also has information about the electronic data interchange model vs the extensible markup language.

Ben Hammersley has written:

'Developing feeds with RSS and Atom' -- subject- s -: Internet programming, Metadata, Web site development, XML - Document markup language -

That depends on what you want to do, xml tools include;

xml parsers

xml validators

xml editors

xml schema editors

xml code generators