Positioning of elements in IMSC1 uses the tts:origin and tts:extent attributes defined in TTML.
These attributes apply to region elements only (see 8.2.7 and 8.2.14 at 2) and have no effect when used on a p or div element.
For example, <p begin="1s" end="2s" tts:origin="47.59% 84.67%" tts:extent="auto">hello</p> will not position the p element at "47.59% 84.67%".
In order to position p or div elements, a separate region element has to be defined for each target position.
For example, the following positions each of the two p elements at different locations:
<?xml version="1.0" encoding="UTF-8"?>
<tt xmlns="http://www.w3.org/ns/ttml" xmlns:tts="http://www.w3.org/ns/ttml#styling">
<head>
<layout>
<region xml:id="pop1" tts:origin="20% 80%" tts:extent="50% 15%"/>
<region xml:id="pop2" tts:origin="50% 80%" tts:extent="30% 15%"/>
</layout>
</head>
<body>
<div>
<p region="pop1" begin="1s" end="2s" >One</p>
<p region="pop2" begin="3s" end="4s" >Two</p>
</div>
</body>
</tt>