I would like to understand how to define and manage projects in PhpED.

I would like to create a project consisting of specified files from within a folder, while excluding some of the files within the same folder. Say a website includes CSS, JS, HTML, PHP, etc., and has a specific root directory. Now imagine that the owner of the site has an event for which they would like to sell tickets. The process of selling those tickets on line will naturally include some of the CSS, JS, HTML, and PHP files within the overall site but not all of them. I would like to create a project that includes only those files that I specify from with the entire site so that I can load the entire project at once without any of the other files within the associated folders that are not involved with subproject processes.

Is this possible with PhpED?

From my point of view, project is something more or less stable in its structure. What you are talking about does not look like a project but a set of projects. And yes it is possible in PhpED.

OK.

How do I go about doing this? I can't find a place with the project management area that allows me to select files to include.

I'd reply with more details if you provide more details on this:

In particular,
1) suppose there is a subset of files belonging to just one ticket. Does it mean that neither of those files belong to any other tickets? In other words, what is the relationship between set of tickets and set of files?
2) suppose you created set of projects and each of them contains necessary set of files. What are you going to do with them after that? In other words, why is it that necessary to keep files belonging to different tickets in different projects?

From my original message:

"I would like to create a project that includes only those files that I specify from with the entire site so that I can load the entire project at once without any of the other files within the associated folders that are not involved with subproject processes. "

That's all I want to do. I just want to be able to load a set of files that are related to one another.

Put them all into one directory or a directory tree and point to the topmost (root) directory in the project properties.
You may have several projects in one workspace, so I believe funtionality you need is covered by the IDE.

I apologize if I'm not communicating this clearly. I'll try it one more time:

Supposing there is a project with all of these files in the same directory.
CommonStuff.php
CommonStuff.css
CommonStuff.js
page1.php
page2.php
page3.php
page4.php
page5.php
page6.php
page8.php

What I would like to do is specify that the following files are related in some way that PhpED recognizes, any way at all, so that PhpEd will open them all at once. And I would like to do this without moving them to another directory first.
CommonStuff.php
CommonStuff.css
CommonStuff.js
page1.php
page2.php
page6.php
page8.php

Then move the rest files from that directory to another and create two projects with those two directories.
PhpED supports extremely huge projects, say 10000 files or more. It would be a nightmare to add them one by one. Hope you got the idea why we support projects on top of directory structure.
Furthermore, think a little about Apache's way. Does it require you to "register" or "add" files for the web? You just tell the directory where your files are and you get them on the web. That's all. Need more webs, just add new virtual host and point it to another directory and so forth.