Can we do SEO for PHP websites? Is it possible to add meta tags and perform SEo on the site
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A PHP website or an ASP.net website will render HTML content. And meta tags are inside the HTML content.
Just as @jok has said "PHP and ASP" do render HTML Content. As an example please look at the following:
On an index.php file You would have something like this;
And your header.php you would look something like this