Fallback Element

If no <Choice> element can be selected, markup consumers shall use the content provided in a <Fallback> element, if present. If no <Choice> element can be selected and no <Fallback> element is provided, the document content is processed as if the <AlternateContent> element were absent.

<Fallback> elements can include the attributes @Ignorable, @MustUnderstand, @ProcessContent, @PreserveElements, and @PreserveAttributes described in this specification. These attributes shall be prefixed when on a <Fallback> element. A markup consumer shall generate an error if it encounters a Fallback element having any unprefixed attribute name.

Note: : A namespace declaration is not considered to be an unprefixed attribute name.

<Fallback> elements might have ignored attributes. Markup consumers shall not generate an error when encountering such attributes. However, markup consumers shall generate an error when encountering an attribute of the <Fallback> element that belongs to a namespace that is neither understood nor ignorable.

Markup producers shall not generate <Fallback> element s that have the @xml:lang or @xml:space attributes. Markup consumers shall generate an error if they encounter the @xml:lang or @xml:space attributes on a< Fallback> element, regardless of whether the element is preceded by a selected <Choice> element.