If you make changes to a DTD file or XML schema associated with an XML file (that is currently open), click XML > Reload Dependencies to update the XML file with these changes. The changes will be reflected in the guided editing mechanisms available in the editor, such as content assist.
For example, you have a DTD file called "Contact.dtd" and an XML file called "Contact.xml" associated with it. Contact.dtd contains a root element called Contact that can contain any of the following children elements: Name, PostalAddress, Email. If you remove the child element Email from the DTD, you will no longer be able to add an Email child element to your root element Contact in your Contact.xml file. This change, however, will not come into effect until you save your changes in the DTD and click XML > Reload Dependencies in the XML editor. Until you click it, you will still be able to add Email elements to Contact.xml.
This feature is very handy when you are making updates to both DTDs and XML schemas and XML files that are associated with DTDs and XML schemas.