I think you are a bit confused on the purpose of custom data attributes. From the w3 spec

Custom data attributes are intended to store custom data private to the page or application, for which there are no more appropriate attributes or elements.

By itself an attribute of data-toggle=value is basically a key-value pair, in which the key is "data-toggle" and the value is "value".

In the context of Bootstrap, the custom data in the attribute is almost useless without the context that their JavaScript library includes for the data. If you look at the non-minified version of bootstrap.js then you can do a search for "data-toggle" and find how it is being used.

Here is an example of Bootstrap JavaScript code that I copied straight from the file regarding the use of "data-toggle".

• Button Toggle

  Button.prototype.toggle = function () {
    var changed = true
    var $parent = this.$element.closest('[data-toggle="buttons"]')
  
    if ($parent.length) {
      var $input = this.$element.find('input')
      if ($input.prop('type') == 'radio') {
        if ($input.prop('checked') && this.$element.hasClass('active')) changed = false
        else $parent.find('.active').removeClass('active')
      }
      if (changed) $input.prop('checked', !this.$element.hasClass('active')).trigger('change')
    } else {
      this.$element.attr('aria-pressed', !this.$element.hasClass('active'))
    }
  
    if (changed) this.$element.toggleClass('active')
  }
  

The context that the code provides shows that Bootstrap is using the data-toggle attribute as a custom query selector to process the particular element.

From what I see these are the data-toggle options:

• collapse
• dropdown
• modal
• tab
• pill
• button(s)

You may want to look at the Bootstrap JavaScript documentation to get more specifics of what each do, but basically the data-toggle attribute toggles the element to active or not.

The data-* attributes is used to store custom data private to the page or application

So Bootstrap uses these attributes for saving states of objects

W3School data-* description

The data-toggle attribute simple tell Bootstrap what exactly to do by giving it the name of the toggle action it is about to perform on a target element. If you specify collapse. It means bootstrap will collapse or uncollapse the element pointed by data-target of the action you clicked

Note: the target element must have the appropriate class for bootstrap to carry out the action

Source action:
data-toggle = collapse //type of toggle
data-target = #myDiv

Target:
class=collapse //I can collapse
id=myDiv

This is same for other type of toggle actions like tab, modal, dropdown