An XML document is organized as a tree of elements. When working on a large document you can collapse some elements leaving in the focus only the ones you need to edit. Expanding and collapsing works on individual elements: expanding an element leaves the child elements unchanged.
Figure: Folding of the XML Elements
An unique feature of Oxygen XML Editor is the fact that the folds are persistent: the next time you will open the document the folds are restored to the last state so you won't have to collapse the uninteresting parts again.
To toggle the folded state of an element click on the special mark displayed in the left part of the document editor next to the start tag of that element or click on the action Toggle fold available from the contextual menu or from the menu The element extent is marked with a grey line displayed in the left part of the edited document. The grey line always covers the lines of text comprised between the start tag and end tag of the element where the cursor is positioned.
Other menu actions related to folding of XML elements are available from the contextual menu of the folding stripe of the current editor:
Close Other
FoldsCtrl NumPad/ (Command NumPad/ on OS
X) -
Folds all the elements except the current element. 
Collapse Child Folds
(Ctrl+Decimal) - Folds the elements indented with one
level inside the current element.-
Expand Child Folds (Ctrl+Equals)- Unfolds all child elements of the currently
selected element. -
Expand
All (Ctrl+NumPad+*) - Unfolds all elements in the current
document. -
Toggle Fold - Toggles the state of the current
fold.
To watch our video demonstration about the folding support in Oxygen XML Editor, go to http://oxygenxml.com/demo/FoldingSupport.html.