The kirby team gave me that line a couple of years ago. Im not sure if its in the docs. I believe @distantnative pointed me in the right direction at the time. He might be able to give some insight here.
// PAGE CONTENT
// Get the a page-field
this.$store.getters["content/values"]()['pagetitle'])
// Update a page-field
this.$store.dispatch("content/update", ["pagetitle", "GREAT SCOTT, now delete me!"])
// BLOCK CONTENT
// Get a block-field
this.content.height_value_em
// Update a block-field
this.$emit('update', {height_value_em: 1})