If you have existing documents with zero indent and you want Oxygen XML Editor to maintain a zero indent when editing or formatting those documents:
Oxygen XML Editor will examine the indent of each document as it is opened and if the indent is zero for all lines, or for nearly all lines, a zero indent will be used when formatting and indenting the document. Otherwise, Oxygen XML Editor will use the indent closest to what it detects in the document.
If you want all documents to be formatted with zero indent, regardless of their current indenting:
All documents will be formatted and indented with an indent of zero.