web/web_widget_x2many_2d_matrix_example/wizard/x2m_matrix.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

    <record id="x2many_2d_matrix_demo" model="ir.ui.view">
        <field name="name">x2m.matrix.demo.wiz</field>
        <field name="model">x2m.matrix.demo.wiz</field>
        <field name="type">form</field>
        <field name="arch" type="xml">
            <form>
                <field name="line_ids" widget="x2many_2d_matrix"
                       field_x_axis="demo_id" field_y_axis="user_id" field_value="value">
                    <tree>
                        <field name="demo_id"/>
                        <field name="user_id"/>
                        <field name="value"/>
                    </tree>
                </field>
            </form>
        </field>
    </record>

</odoo>