Where are the docs for the `this.field` function?

I’m seeing a lot of examples that use this.field as a function within a computed Vue function. For example, in this cookbook example: Block factory: Creating your own blocks collection | Kirby CMS

we see:

      computed: {
        textField() {
          return this.field("text");
        }
      }

I’ve looked in the Vue.js docs as well as the limited Kirby docs, but I can’t find mention of this function anywhere.

Is the this.field function documented anywhere?

No.

This is in the context of a block, where this refers to the block, and field('text') to the field text defined within the block.

Examples can be found here:

Is this functionality is provided by Kirby itself?

Perhaps someone could point me to that part of the code?