class_ = if want to use class(reserved key) as an attribute(variable) need to use class_(underscore)

flask:

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clear cache on the web browser & show updated changes

on the browser:

shift + refresh button

2.If we want to edit any website template oneline on any web browser:

right click > inspect > console >cmd:

document.body.contentEditable=true + Enter

Then we can edit anything online & want see the same changes from next time need to: right click > save the file > replace the index.html with changed filename.html