xml:space 

<div>
  <h3>space (as an attribute name)</h3>
  <p>denotes an attribute whose value is a keyword indicating what whitespace processing discipline is intended for the content of the element; its value is inherited. This name is reserved by virtue of its definition in the XML specification.</p>
</div>

Attribute Information

Used By

Attribute Group xml:specialAttrs
Elements code, glyph-data, preformat, x

Source 

<xs:attribute name="space">
  <xs:annotation>
    <xs:documentation>
      <div>
        <h3>space (as an attribute name)</h3>
        <p>denotes an attribute whose value is a keyword indicating what whitespace processing discipline is intended for the content of the element; its value is inherited. This name is reserved by virtue of its definition in the XML specification.</p>
      </div>
    </xs:documentation>
  </xs:annotation>
  <xs:simpleType>
    <xs:restriction base="xs:NCName">
      <xs:enumeration value="default"/>
      <xs:enumeration value="preserve"/>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>

Sample