Print some variables in the named template page
First:
Second: {SECOND|strtoupper}
Third: {THIRD}

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Let's go to a nested and fetch the variables from the named template page
page.First:
page.Second: {SECOND|strtoupper}
page.Third: {THIRD}

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Let's go to another nested template and fetch the variables from the parent template
First:
Second: {SECOND|strtoupper}
Third: {THIRD}

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Let's go to another nested template and let the variable mdifiers decide where to get the variables from
First:
Second:
Third:

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Last but not least the original value of the variables in template page
First: {FIRST}
Second: {SECOND}
Third: {THIRD}