Adding a time period to all entities

I'd like to write a plugin that adds a time period to any kind of content posted. So, if I tell a story in a blog post that took place between 2016/Dec/24 and 2017/Jan/04, I'd like to be able to add that information to the post. Or if I create a photo album that contains pictures from 1999 to 2001, I'd like to attach that information to the photo album.

Ultimately, I want to use that information to create an interactive timeline that displays any content from whatever time period I select.

I've read some of the developer docs, and I get the basics of how to create a new entity type. But I'm really not sure where to start on just adding information to an entity without having to clone every entity type to customize it...

I have written applications in PHP, but the past few years have had me doing sysadmin and devops work. Lots of deploying software, using Ansible, etc. Not so much web development. So a few pointers on how to get up to speed on how Elgg works enough to build what I described would be much appreciated.

'Course, if there's a plugin I wasn't able to find that actually does this, please point it out. :)

Thanks!

Beginning Developers

Beginning Developers

This space is for newcomers, who wish to build a new plugin or to customize an existing one to their liking