I'm trying to create a function on functions.php theme file to add reCaptcha form HTML (available at Custom Theming), but I didn't find an appropriate hook at Filter Reference or at Action Reference to use with add_action().
I know that there are a lot of plugins to do it. I don't want to use a plugin because I want it to be customizable. And I don't want to edit comments.php on my theme either.
All this is because I want to validate reCaptcha input with jQuery before the form is actually sent, like in my Contact page.
So far, what I need to know is if there is a tag (either a hook or filter) to use in add_action() that runs when the comment form html is sent to the browser.