why do I need to check the HTML shown to the user for taint?
Same reason, security. From the docs:
force_untaint - if set to 1 the module will not allow you to set unescaped parameters with tainted values. If set to 2 you will have to untaint all parameters, including ones with the escape attribute. This option makes sure you untaint everything so you don't accidentally introduce e.g. cross-site-scripting (CSS) vulnerabilities. Requires taint mode. Defaults to 0.

In reply to Re^3: Is the force_untaint option in HTML::Template overkill? by Anonymous Monk
in thread Is the force_untaint option in HTML::Template overkill? by SilasTheMonk

Title:
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