What Is the xml:space Attribute in XML?

The xml:space attribute is a reserved attribute in the XML standard that signals to an XML parser or consuming application how whitespace characters within an element should be handled. By default, XML parsers may strip, collapse, or alter insignificant whitespace such as line breaks, tabs, and multiple spaces. This article explains the purpose of the xml:space attribute, the two valid values it accepts, how inheritance works across nested elements, and its practical importance for maintaining data integrity.

Purpose of xml:space

In standard XML processing, whitespace between tags or within text nodes is often normalized or stripped to reduce file size and simplify parsing. However, certain types of data—such as source code snippets, poetry, tabular text, or formatted documents—rely strictly on exact spacing and indentation.

The xml:space attribute was defined directly in the W3C XML specification to standardize how authors declare their whitespace preservation requirements without relying on proprietary or application-specific flags.

Supported Values

The xml:space attribute accepts only two standard values:

  1. default: Tells the application that its standard whitespace handling rules apply. In this mode, the parser or application is free to remove or collapse redundant whitespace.

    <paragraph xml:space="default">
    This text can have its extra spaces collapsed.
</paragraph>

  2. preserve: Explicitly instructs the application to maintain all whitespace characters (spaces, tabs, carriage returns, and line feeds) exactly as they appear within the element.

    <code-block xml:space="preserve">
    function example() {
        return true;
    }
</code-block>

Inheritance and Scope

The xml:space attribute applies to the element on which it is declared and recursively inherits down to all child elements.

If a parent element defines xml:space="preserve", all nested tags will preserve whitespace unless a child element explicitly overrides the behavior by setting xml:space="default".

<document xml:space="preserve">
    <formatted-text>
        Spaces and line breaks are preserved here.
    </formatted-text>
    <unformatted-text xml:space="default">
        Spaces are handled by the application's default rules here.
    </unformatted-text>
</document>

Schema and DTD Requirements

Because xml:space is an official reserved attribute belonging to the xml namespace, it must be properly declared in a Document Type Definition (DTD) or XML Schema (XSD) if validation is enabled.

In a DTD, it is typically declared as an enumerated type:

<!ATTLIST pre xml:space (default|preserve) "preserve">

In an XML Schema, it is referenced via the standard XML namespace:

<xs:attribute ref="xml:space" default="preserve"/>

Key Significance in XML Workflows