DocumentID: ECMA-376/Part5/9.1.4
Title: ECMA-376, Part5: 9.1.4 MustUnderstand Attribute
Extracted-From: ECMA-376 Office Open XML File Formats, 1st Edition / December 2006
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9.1.4 MustUnderstand Attribute

The MustUnderstand attribute value containsa whitespace-delimited list of namespace prefixes identifying a set of namespace names. A markup consumer that does not understand these identified namespaces shall not continue to process the markup document, regardless of whether the non-understood namespace was identified as an ignorable namespace on an ancestor element. Markup consumers shall generate an error condition if one or more of these identified namespaces is not understood.

The value of the MustUnderstand attribute can be an empty or blank string. When a markup consumer encounters such a value, it shall proceed as if the MustUnderstand attribute was not declared.

[Note: §9.2 clarifies the rules for processing the MustUnderstand attribute when it is applied to a Choice or Fallback element, or when it is applied to a descendant element of one of those elements. end note]

[Example: Example 9--4. Processing an attribute's prefixed qualified name

The declaration of a Version 2 attribute causes a Version 1 markup consumer to trigger an error when processing the last Circle element.

<Circles
  xmlns=""
  xmlns:mc="
"
  xmlns:v2="http://schemas.openxmlformats.org/Circles/v2">

  <Circle Center="0,0" Radius="20" Color="Blue" />

  <Circle Center="25,0" Radius="20" Color="Black" />

  <Circle Center="50,0" Radius="20" Color="Red" />

  <Circle Center="13,0" Radius="20" Color="Yellow" />

  <Circle Center="38,0" Radius="20" Color="Green"
    v2:Opacity="0.5" />
</Circles>

Example 10--5. Processing a MustUnderstand attribute

The value of the MustUnderstand attribute causes a Version 1 markup consumer to trigger an error when processing the root Circles element.

<Circles
  xmlns="http://schemas.openxmlformats.org/Circles/v1"
  xmlns:mc=

  xmlns:v2="http://schemas.openxmlformats.org/Circles/v2"
  mc:MustUnderstand="v2">

  <Circle Center="0,0" Radius="20" Color="Blue" />

  <Circle Center="25,0" Radius="20" Color="Black" />

  <Circle Center="50,0" Radius="20" Color="Red" />

  <Circle Center="13,0" Radius="20" Color="Yellow" />

  <Circle Center="38,0" Radius="20" Color="Green"
    v2:Opacity="0.5" />
</Circles>

end example]