I want to author a tag in page properties of all the pages present under one node. It's very difficult to open page properties of each page and author the tag.
Can it be done by using bulk editor?
Yes, it can be done using bulk editor.
For the query parameters field, use GQL like the below sample
The double quotes and single quotes can be very specific for specific properties.
For multiple tags, use space after the comma
Yeah,creating a new tag and applying to multiple pages under the same node in classic UI.
You can use the Page properties bulk editor to update page properties of multiple pages at one time.
 Configuring your Page for Bulk Editing of Page Properties
By "authoring tag" are you referring to tagging multiple pages with an existing tag under the same node OR creating a new tag and applying to multiple pages under the same node ?