Controlling state of checkbox programatically

I am relatively new to PHP and I'm struggling with how to control checkboxes on my forms.
I have a group of 6 related checkboxes on a form - there are some other unrelated checkboxes on the form too - and I want all of the six related checkboxes to be checked initially. When the user completes the form, they may very well uncheck one or all of the six checkboxes and that is fine.

Various edits take place on the various text inputs and text areas on my form and any error will cause the...

Controlling state of checkbox programatically

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