Why I can not use this xpath (can you only use @name inside expr, but not string? Because that page does not have attribute name)?:

            <xpath expr="//page[@string='Internal Notes']" position="after">
                <page string="Laser Damage Testing">
                    <field name="substrate_id"/>
                </page>                    
            </xpath>

Strangely it install my module with this view, but if I try to upgrade my module I get this error:

InternalError: current transaction is aborted, commands ignored until end of transaction block

Then I can't do anything in my database, always getting this error. I can fix it only by restoring to older database.

If I use this:

<page string="Internal Notes" position="after">
                    <page string="Laser Damage Testing">
                        <field name="substrate_id"/>
                    </page>
                </page>

Then it work fine. But if I want to insert fields in different parts of the view, I need to use xpath.