The property groups are sets of key/value configuration which have been labeled together in a group.
Once labelled these can be looped over as part of the template tag syntax.
Groups can contain an identity which is a pre-defined key with the value you provide. This means a property group will always have the identity as a key/value property.
A property group can also be defined with multiple labels, but this syntax is much more verbose
<Structure xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
...
<PropertyGroups>
<PropertyGroup label="Group" identity="1">
<Property name="GroupKey1">GroupValue1</Property>
<Property name="GroupKey2">GroupValue2</Property>
</PropertyGroup>
<PropertyGroup label="Group" identity="2">
<Property name="GroupKey1">GroupValue1</Property>
<Property name="GroupKey2">GroupValue2</Property>
</PropertyGroup>
<PropertyGroup identity="1">
<Labels>
<Label>Label1</Label>
<Label>Label2</Label>
</Labels>
<Properties>
<Property name="GroupKey1">GroupValue1</Property>
<Property name="GroupKey2">GroupValue2</Property>
</Properties>
</PropertyGroup>
</PropertyGroups>
...
</Structure>