text: Why does the arccatalog ISO XML not include "gmd" within XML tags but other examples I have found online do?
  I.e. My ISO 19115 records from Arc Catalog have tags like <fileIdentifier>, but I have seen many others where the tags are written as <gmd:fileIdentifier>. What is causing this difference?
  Here are a couple screen shots. The first is from a record that I have exported from ArcCatalog in ISO NAP, the second is an example of a record I found online from NOAA.
  gmd refers to a namespace for geospatial metadata XML tags. I believe using these tags requires a higher version of the XML standard (2.0) than the XML parser ArcGIS uses.
  Namespaces are supported by higher XML tools like Oxygen and other software that supports XML 2.
  XML Namespaces