The XML Recommendation defines whitespace as a single term for the space, tab, and linebreak characters which may appear in a document. When such characters appear in a document as content of a text node, XML generally considers them significant and requires that a processor preserve all of them. However, when an element is defined as containing only other elements, the usual expectation is that any white space characters adjacent to the markup tags used to delimit those elements are not significant and may be ignored by an XML processor. This does not, of course, apply to whitespace characters within an element containing mixed content, which must be preserved. Hence, in a document like the following apple pie banana custardcarrot cake the white space between the first and second items, and that between the second and third, is significant only if the content model for list permits text as well as item elements. The spaces within individual items are however always significant.

A further complication is that some XML processors, notably XML editors, may introduce white space in a document to enhance its readability when it is displayed.

Most TEI elements are defined as having mixed content, and for the most part TEI markup appears at places in a document where the presence or absence of whitespace is not in any case significant. The xml:space attribute is therefore of little importance. There are however a few situations in which it may be essential, typically where complex markup is being worked on by a tool which introduces whitespace in order to enhance display of the text.

For example, when transcribing an inscription with the elements described in chapter , a single word may well gain several additional tags to mark parts of the word which are supplied or conjectural. Such tags do not interrupt the word however, and hence introducing space where they occur would be misleading. The value of preserve for the xml:space attribute on the parent div element may be used to indicate that all and only the spaces actually present in the XML source should be regarded as significant; an editor is not then permitted to introduce additional spaces.