<componentGrp> (component group) – The child elements of this element are treated as parts of the elements header. Although this is an implicit way of expressing FRBR's hasPart / isPartOf -relationships, it avoids this terminology in order to prevent confusion with musical terminology. All children of a component must be the same type as its parent: works within work, items in item, etc.
Module MEI.frbr
Contained by
MEI.frbr: expression item
MEI.header: source work
May contain
MEI.frbr: expression item
MEI.header: source work
element componentGrp
    | model.expressionLike*
    | model.manifestationLike*
    | model.itemLike*

<sch:rule context="mei:componentGrp">

<sch:assert test="every $i in ./child::mei:* satisfies $i/local-name() eq ./parent::mei:*/local-name()">Only child elements of the same name as the parent of
the componentGrp-element are allowed.</sch:assert>

MEI Guidelines Version 2.1.1

MEI Elements