Insert <h2>Hello</h2> at the beginning

gistfile1.js

var html = '<h2>Hello</h2>',
	htmlDoc = ve.createDocumentFromHTML( html ),
	newDmDoc = ve.dm.converter.getModelFromDom( htmlDoc ), // Omitting targetDoc here, which may cause issues with link hrefs
	surfaceModel = ve.init.target.getSurface().getModel(),
	tx = ve.dm.Transaction.newFromDocumentInsertion( surfaceModel.getDocument(), 0, newDmDoc ); // 0 means insert at the beginning

surfaceModel.change( tx );