Plugin that allows you to insert a table of contents into your posts.
https://wordpress.org/plugins/easy-table-of-contents/
Widgets · WordPress Plugins
Get access to data on 697,463 websites that are Easy Table of Contents Customers. We know of 281,053 live websites using Easy Table of Contents and an additional 416,410 sites that used Easy Table of Contents historically and 135,363 websites in the United States.
Get a list of 697,463 websites using Easy Table of Contents which includes location information, hosting data, contact details, 281,053 currently live websites and an additional 134,749 domains that redirect to sites in this list. 416,410 sites that used this technology previouslyand 135,363 websites in the United States currently using Easy Table of Contents.
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