Where to find documentation for CPT block template? (PHP)

I have been searching for a day and still carn’t seem to find the right documentation for what arguments I can pass to core components when attempting to configure a CPT block template in php. This is what I have but I want to take this further by nesting buttons and custom html etc. but carnt find the docs I need.

'template' => array(
    array( 'core/columns', array(), array(
        array( 'core/column', array("width" => "60"), array(
            array( 'core/image', array() ),
        ) ),
        array( 'core/column', array("width" => "40"), array(
            array( 'core/image', array() ),
            array( 'core/heading', array(
                'placeholder' => 'Add a inner paragraph'
            ) ),
        ) ),
    )
)       

Found everything needed to create bespoke blocks in JSX but blegh, Not got the time to learn the wizardry ways of JSX just yet and I dont really want new blocks just want the existing one bound as a template to a custom post type.

A good way to example my question, how did this person find the answer on how set the width of this template columns.

How to set column widths in a CPT block template?

How did the person find this answer ? did they have to dive in to the JS scripts of the component and work it out or is there some documentation on this or am I missing something all together.

Any help would be greatly appreciated.

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Author: Johnny