White Space in Element Content

The XML DOM has three methods for accessing the text content of elements:

Note   White space consists of newline, tab, and space characters.

The nodeValue property always returns what is in the original document independent of how the document is loaded and current xml:space scope.

The text property concatenates all text in the specified subtree and expands entities. This is dependant upon how the document is loaded, the current state of the preserveWhiteSpace switch, and the current xml:space scope, as follows:

preserveWhiteSpace = true when the document is loaded

preserveWhiteSpace = false when the document is loaded

Where preserved means the exact original text content as found in the original XML document, trimmed means the leading and trailing spaces have been removed, and half preserved means that "significant white space" is preserved and "insignificant white space" is normalized. Significant white space is white space inside of text content. Insignificant white space is white space between tags as follows:

<name>\n
\t<first>    Jane</first>\n
\t<last>Smith     </last>\n
</name>

In this example, the red is insignificant white space and can be ignored, while the green is significant white space since it is part of the text content and therefore has a significant meaning and cannot be ignored. So in this example, the text property returns the following results:

Notice that "half preserved" normalizes insignificant white space, for example, the newlines and tab characters are collapsed down into a single space character. You can change the xml:space attributes and the preserveWhiteSpace switch and the text property will return a different value accordingly.

CDATA and xml:space="preserve" subtree boundaries

In the following example, the contents of the CDATA node or the "preserved" node are concatenated as they are and do not participate in the insignificant white space normalization. For example:

<name>\n
\t<first> Jane </first>\n
\t<last><![CDATA[     Smith     ]></last>\n
</name>

In this case, the white space inside the CDATA node is never "merged" with "insignificant" white space and is never trimmed. Therefore, the "half preserved and trimmed" case will return the following:

"Jane     Smith     "

Here, the insignificant white space between the </first> and <last> tags is included independent of the contents of the CDATA node. The same result is returned if the CDATA is replaced with the following:

<last xml:space="preserve">     Smith     </last>

Entities are special

Entities are loaded and parsed as part of the DTD and appear under the DOCTYPE node. They do not necessarily have any xml:space scope. For example:

<!DOCTYPE foo [
<!ENTITY Jane "<employee>\n
\t<name> Jane </name>\n
\t<title>Software Design Engineer</title>\n
</employee>">
]>
<foo xml:space="preserve">&Jane;</foo>

Assuming that preserveWhiteSpace=false (in the scope of the DOCTYPE tag), the insignificant white space is lost when the entity is parsed. The entity will NOT have white space nodes. The tree will look like this:

DOCTYPE foo
    ENTITY: Jane
        ELEMENT: employee
            ELEMENT: name
                TEXT: Jane 
            ELEMENT: title
                TEXT>:Software Design Engineer
    ELEMENT: foo
       ATTRIBUTE: xml:space="preserve"
       ENTITYREF: Jane

Notice that the DOM tree exposed under the ENTITY node inside the DOCTYPE does NOT contain any WHITESPACE nodes. This means that the children of the ENTITYREF node will also have no WHITESPACE nodes even though the entity reference is in the scope of xml:space="preserve".

Every instance of an ENTITY referenced in a given document always has the identical tree.

If an entity absolutely must preserve white space then it must specify its own xml:space attribute inside itself or the document preserveWhiteSpace switch must be set to True.