What does the value represent in SVG when animating shapes?

Question

For example what is 300 and 0 value in this code? <svg width="1000" height="250">
<rect width="150" height="150" fill="orange">
<animate attributeName="x" from="0" to="300"
dur="3s" fill="freeze" repeatCount="2"/>
</rect>
</svg>

Answer 1

There a orange rectangle will be move from 0px to 300px second time.