Open Page in Lineup

Explain what this code does.

function handler(event) { let title = event.target.innerText let message = { action:"doInternalLink", title: "Json Schema", keepLineup: event.shiftKey } window.parent.postMessage(message, "*") }

output.innerHTML = `<button> Open Existing Page </button>` output.addEventListener("click", handler)

//wiki.ralfbarkow.ch/assets/pages/snippet-template/basicjs.html?snippet-template HEIGHT 200