Adding more Custom field TYPES-- modded by necessity
I needed more Custom Field types because expanding the Custom Fields beyond text, text area, and drop-down is THE most indispensable KEY to expanding ClassiPress beyond "just" a Classified Ads theme. Once you have options beyond the rudimentary "big 3 -- text, text area, drop-down" then you can with ONE custom field store and make multiple selections available to the Ad Poster which can ultimately be posted as bulleted lists of Features or whatever that list represents.
So, I had to mod away and now have at least the capability of selecting a "checkbox" when creating a new custom field for a custom category form. That one mod means that I can type in comma-separated field values and they are instantly saved as individual checkboxes so that in my new custom form for a particular ad category a new Poster can check individual values to help quickly explain features pertaining to this category.
For instance, if the Ad Category is House Rental, then the form can display over and over the same list of features for that House that the user can quickly select with a click if they apply to the rental house. Also, by including this custom field I can set up a separate custom search function that only has to query one custom field in multiple ads if it presents values that would be popular searches for ads.
I am no PHP wiz, but I have made this work. And as difficult as it was for me because I am not a coder and because I am not familiar with the logic the developers have used when making decisions about what to code and how to code it, if little ole me could do this in a day from knowing nothing then it is a proverbial "piece of cake" for the developers themselves to dive in and extend the capabilities of the Custom Form/Custom Fields code in both the save, edit, and display files.