### begin

    // Entity stuff, e.g., in case of m being a Matrix:
    begin( m, tag::addressing_index<1>() )  // Row iterator, only dense types supported at the moment
    begin( m, tag::addressing_index<2>() )  // Column iterator
    begin( m, tag::row() )            // Same as <1>
    begin( m, tag::column() )         // Same as <2>
    begin( m, tag::major() )          // Depends on data_order
    begin( m, tag::minor() )          // Depends on data_order

    begin( m, tag::index_major() )            // Sparse matrices
    begin( m, tag::index_minor() )            // Sparse matrices
    begin( m, tag::compressed_index_major() ) // Sparse matrices

    // Data stuff, e.g.,:
    begin( m, tag::value() )          // Begin of value array or main diagonal

    // Convenience
    begin1(m)                       // Convenience for tagged version
    begin2(m)                       // Convenience for tagged version
    begin_row(m)                    // Convenience for tagged version
    begin_column(m)                 // Convenience for tagged version
    begin_major(m)                  // Convenience for tagged version
    begin_minor(m)                  // Convenience for tagged version

    begin_index_major(m)            // Convenience for tagged version
    begin_index_minor(m)            // Convenience for tagged version
    begin_compressed_index_major(m) // Convenience for tagged version

    begin_value(m)                  // Convenience for tagged version