Mondrian 4 documentation

I am about to start creating OLAP using Mondrian. Is there an official Mondrian 4 documentation? The documentation I found at mondrian.pentaho.com/documentation doesn't seem to cover the latest Mondrian version. I thought virtual cubes are replaced by measure groups. See an actual documentation stub below:

<Schema>
    <Cube>
        <Table>
        ...
        <Dimension>
        <DimensionUsage>
        <Measure>
        <MeasureExpression>
    ...
    <VirtualCube>
        <CubeUsages>
        <VirtualCubeDimension>
        <VirtualCubeMeasure>

Is there any other source or tutorial where can I start with Mondrian 4?

The Mondrian documentation you mentioned is for older version - Mondrian 3.

There is a Mondrian 4 documentation.

Check the documentation stub:

<Schema>
    <PhysicalSchema>
        <Table>

    <Cube>
        <Dimensions>
        ...
        <MeasureGroups>
            <MeasureGroup>
                <Measures>
                ...