rendering elements for SVG in SVG tag

I have SVG file where there is a svg tag inside a svg tag please refer below svg file for better understanding. I want to know the logic or algorithm which a svg viewer use to display the file. .i.e how it manipulates the value of outer SVG
width="8.5in" height="11in" viewBox="0 0 612 792" with the values of height="900" width="200" x="0" y="0 and viewBox="0 0 524.29 313.79" which are inner SVG tags.

please help in this regards

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