Elements in the input that participate in a named flow must be identified with css:flow attributes. '::footnote-call', '::duplicate' and '::alternate' pseudo-elements must be reprented by css:footnote-call, css:duplicate and css:alternate elements with a css:anchor attribute that points to the original element.

The document on the 'result' port represents the normal flow. Elements that participate in a named flow are replaced with an empty css:_ element with a css:id attribute. The css:id attribute is either taken from the element that is moved to the flow, or generated. If the element is a css:duplicate or css:alternate, there is no replacement. If the element has an associated css:footnote-call or css:alternate pseudo-element that remains in the normal flow, there is also no replacement, and the pseudo-element gets a css:id attribute.

All elements in the input document that participate in named flows are extracted, grouped according to flow, and inserted into documents on the 'flows' port, one document per flow. Elements within the same flow become siblings with a common css:_ parent element, which is the document node of that flow. Elements are ordered according to the original document order. The document node gets a css:flow attribute that identifies the flow. Other css:flow attributes are dropped. Elements get a css:anchor attribute that matches the css:id attribute of the (css:_, css:alternate or css:footnote-call) replacement element at the original position (which may be in the normal flow or in a named flow). Elements that already have a css:anchor attribute don't get a new one. Elements with an associated css:alternate pseudo-element at the original position get an css:anchor attribute that matches the css:id attribute of the the pseudo-element. Style attributes are added in the output in such a way that for each element, its computed style at the output is equal to its computed style in the input. Similarly, xml:lang attributes are added to the elements.