Setting a document's title to be its name/id

Currently for several doctypes the title is the customer by default. However we often sell to the same customer. A more effective title would be the document name. {name} and {id} don’t work. How do I reference the document name from another field?

Also, the documentation says “If you want a fixed title, you can set the rule in the Options property. In this way, the title will be automatically updated every time the document is updated.” however when I try setting “Options” that instead of “Default” on the title data field, suddenly I can no longer open documents of that doctype and I have to revert that field’s setting.

EDIT: even stranger, this document:
says you can use HTML or read-only type field as a title field, but this document:
says it has to be a data type field.

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I am looking for solution to this problem