The event_rules manifest property provides a mechanism to add rules that intercept, block, or modify web requests in-flight using declarativeWebRequest or take actions depending on the content of a page, without requiring permission to read the page's content using declarativeContent.
Translating rules from javascript to manifest
The following defines a rule to display a page action if the current page has a video css tag in javascript:
chrome.declarativeContent.onPageChanged.addRules([{ actions: [ new chrome.declarativeContent.ShowPageAction() ], conditions: [ new chrome.declarativeContent.PageStateMatcher( {css: ["video"]} ) ] }]); This is the same definition in the manifest:
{ "name": "Sample extension", "event_rules": [{ "event": "declarativeContent.onPageChanged", "actions": [{ "type": "declarativeContent.ShowPageAction" }], "conditions": [{ "type": "declarativeContent.PageStateMatcher", "css": ["video"] }] }], ... }