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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:

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"]

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