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Dexter N Muir
A more thorough explanation, then:
"their" is possessional - it's the plural of "his/her/its"
"there" is positional - in this case the position/place is in the code and eventually on screen.
They sound the same but have vastly different meanings. This is partly American dialect and partly sub-standard education - not your fault, but your teachers in childhood and the system they operate in. It's akin to "your/you're" and even "yaw", and that dreadful "y'all". Really, don't get me started ... do 100 centers make a dollarer? and where the 'ell is the "L" in sodder and goff?