Entity References are Expanded and Not Preserved

 

When the entity reference is expanded and replaced by the text it represents, the XmlEntityReference node is not created. Instead, the entity declaration is parsed, and nodes created from the content in the declaration are copied in the place of the XmlEntityReference. Therefore, in the &publisher; example, the &publisher; is not saved, but instead, an XmlText node is created.

expanded tree structure
Tree structure for entity references that are expanded

Character entities such as B or < are not preserved. Instead, they are always expanded and represented as text nodes.

To preserve XmlEntityReference nodes and child nodes of the entity reference attached to it, set the EntityHandling flag to ExpandCharEntities. Otherwise, leave the EntityHandling flag at the default, which is to ExpandEntities. In this case, you will not see entity reference nodes in the DOM. The nodes are replaced by the nodes that are copies of the child nodes of the entity declaration.

One side effect of not preserving entity references is that when the document is saved and passed on to another application, the receiving application does not know that the nodes were generated by an entity reference. However, when entity references are preserved, a receiving application sees an entity reference and reads the child nodes. It is apparent that the child nodes represent the information that was in the entity declaration. For example, the DOM theoretically has the following structure if entity references are preserved.

XmlElement: publisher

XmlEntityReference: &publisher;

XmlText: Microsoft Press

If entity references are expanded in the DOM, which is the default method, the structure has this type of tree:

XmlElement: publisher

XmlText: Microsoft Press

Notice that the entity reference node is gone, and the receiving application cannot tell that the XmlText node containing "Microsoft Press" was created from an entity declaration.

If you use a reader that cannot resolve entities, the Load method throws an exception when it encounters an entity reference.

XML Document Object Model (DOM)

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