Generating an XML file from HTML form input

Question

I am trying to generate an XML document from html form input using PHP all on a LAMP stack. I can generate the XML document, but I seem to be having problems brining in the data from the html field.

I am trying to call $_POST['itemName'] as a text item in my PHP code, but I am getting an error that says that itemName is undefined. Please see the partial index.html document and full generate.php code below:

Here is the full `generate.php` code:

<?php

$dom = new DomDocument('1.0'); 

$orders = $dom->appendChild($dom->createElement('orders')); 

$order = $orders->appendChild($dom->createElement('order')); 

$item = $order->appendChild($dom->createElement('item'));

$item->appendChild($dom->createTextNode($_POST['itemName']));

$dom->formatOutput = true;
$orders = $dom->saveXML();
$dom->save('orders.xml');

?>

Here is the form section from index.html:

<form name="form1" action="generate.php" method="post">
    <input type="text" class="form-control" id="itemName" 
    placeholder="Item Name">

    <button type='submit' action='submit' name='generate'>Generate XML</button>
</form>

I expect to get an XML document like this:

<?xml version="1.0"?>
<orders>
  <order>
    <item>text from form field</item>
  </order>
</orders>

What I get is the following error displayed in the browser:

Notice: Undefined index: itemName in generate.php on line 17

I have test the Apache Server and PHP on my local machine, and it works correctly, so the problem definitely lies within my code.

I feel like this is really simple and I am making a pretty obvious mistake, but I don't really know PHP, so this is all kind of new to me.

Thanks!