Convert xml to MAP in php using simplexml, NOT json - php

Question

I'm trying to figure out how to take a simple custom xml file (its actually an EML file, but simpeXML works with it anyway) and take tagnames and the text that follows (i think simpleXML calls them children) and put them into a MAP, with key/value pairs. I've looked at some examples on this site and others about converting to arrays and such but they all seem extremely complicated for my needs. I should note that my custom xml does not contain ANY attributes and this conversion only needs to work with MY custom xml file and not any others ever.
So a simple example of my eml file is here
<lesson>
<unit>4</unit>
</lesson>
So then basically what I would want is a MAP, or whatever a key/value collection is called in php that would give me:
Map[0](lesson,null)
Map[1](unit,4)
It's important that I get the null values (or an empty string is ok too), so I can verify that the eml file is valid. I need to validate it with php, not using a namespace validator or a dtd file or however that is done. So the first key/value pair, or the root tag, HAS to be lesson, and then ill also verify that there is a unit tag, then a title tag, then at least one other type of tag etc...I can do that easy if i can get everything into a key/value collection. Also, there are many tagnames that are the same, so keys should be not-unique. However for the value, they should be unique, but only to the tag name. So unit can only one one "4", but another tag, lets say imageID could also have "4". This is not a requirement but a "nice to have" and I can probably figure that out if its not simple. But if its REALLY hard then I will skip it all together.
I hope this makes sense.
And no, I don't think Im allowed to use json. I'm sure it can be done in simpleXMl but if its impossible, then please provide a method to do it in json (assuming that json is included with PHP and not an extension that has to be loaded).
This is university homework, so I can't use extensions or anything else that would require anything beyond what comes with the XAMPP basic package (php, mysql, apache etc...).

Answer 1

Really surprised I got no votes or views or answers or anything on this. I did figure this out in the end. Oh yeah...got the tumbleweed badge for this too!
Anyway the answer was actually quite simple. I used the simplexml_load_file function in PHP which actually supports any kind of xml-style. So after running this,
$eml = simplexml_load_file("unit.eml");
I then did things like this
foreach ($eml->children() as $child)
$tag = $child->getName();
$tagInfo = $child;
And used $tag and $tagInfo to iterate through my eml and get everything I needed.