_DEFAULT_ link and node are built-in - the default defaults
All others are initially empty, with just a reference to the parent.


Per node:
	list of properties
	for each:
		name
		value
		config filename (if any)
		config line number (if any)
		type? (so we can use a standard parser/writer)
	special name/type for comments

editor has set/get functions to alter the config.
all map fns need to use the getter to get config info
seperate array of nodes and links (as now) for *runtime* info
 - e.g. the width of the image, the calculated position, the ReadData results	
 - also store some kind of reference to the appropriate place in the DOM

To avoid PHP4 reference rubbish, each DOM item is just stored in an array with a UID. The UID is used as a reference whenever one is needed. No circular references, no accidental pass-by-value. Use uniqid().

WriteConfig then just enumerates the DOM.

Maybe need a function to optimise the tree, making sure that the property value doesn't match the parent's value (i.e. it's redundant)

LINK _DEFAULT_
	LINK DEFAULT
		LINK l1
		LINK l2
		LINK l3
		LINK template1
			LINK l4
			LINK l5
			LINK l6

NODE _DEFAULT_
	NODE DEFAULT
		NODE n1
		NODE n2
		NODE n3
		NODE template1
			NODE n4
			NODE n5
			NODE n6
		NODE template2
			NODE n7
			NODE template2a
				NODE n8
		NODE template3