int xmlWriterSetIndent(xmlWriter writer, int indent
[, string indentString])
0(default) - do not indent
1- indent output
indentString(optional) - What string to use for indenting. The default is a single space.
xmlWriterSetIndent() sets writer to automatically apply
line breaks and spaces between XML elements to give an indented
structure to the XML file.
Note that all spaces between XML elements are significant and
technically doing this changes the contents of the XML file (see the
xmlTree Text Nodes and Children (here)
<$ret = (xmlWriterSetIndent($writer, 1, ' '))>