@TW_Tones I’m not gonna go so far as to ask you (or anyone else) to design a solution for me.
I was actually looking to make a suite of widgets for building UIs, many of which wrap the existing widgets (edit-text, etc.) but also can be passed conditions (filters) which display validation messages (I used $error for the example, but I intend them to look and behave differently). And I wanted the validations to have actual force, without changing the button every time I change one of the conditions.
Maybe the best TW way to do this is to add pragmas (\define or \procedures) for all the filters and reference all the same filters in the button to disable it. But I was trying to avoid having to add everything to both the button and whatever field is using them… too easy to forget to add or remove it from one thing and then have a mismatch.
Thus, I was looking for a way for the button to detect the presence of the error messages without having to change the code for the button every time I add or remove code for an error message elsewhere. (I looked to see if there was some way, even if only in action widgets, that I detect DOM nodes with a CSS selector or XPATH selector, but I couldn’t find a way other than wikify.)
I thought about having the custom input widgets record the valid/invalid values into state tiddlers which the custom button widget could lookup, but the problem is that the same fields could change due to things outside the custom input widget. So I thought, the custom input widgets would just need to listen for changes to the fields, and update the validation states on any changes to those fields regardless of the origin/cause. But I found a topic you created where it was answered that there was no such mechanism.
Maybe I am just trying to do something that TW isn’t designed for. One thing it doesn’t seem to be great for is modularization (in this case, the button being modular in the sense that it doesn’t have to know the conditions that cause validations to appear, only whether there are any).
Alternatively, maybe I could look into whether a custom solution with JS could detect DOM nodes - although, outside of action strings, this seems problematic. (Or maybe a custom JS plugin could allow for field listeners, although that seems like a potentially more complicated solution than wikification, and potentially similarly performance-intensive.)