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Browser compatibility and issues

While scheme-relative URLs are the Jedi Masters of flexibility, execute your tests across various browsers. Compatability with big players like Firefox, Safari, IE6, IE7, and Opera is well-documented, but remember, always two, there are, a master and an apprentice- browser and edge cases.

• Convenience over Complexity: A one-size-fits-all solution for both HTTP and HTTPS.
• Mixed Content Warnings: Avoid the "dark side" of content issues, especially in browsers like IE8.
• Version-Specific Problems: Beware of IE7 and IE8 are known to double-download CSS with protocol-relative URLs.

The force of protocol-relative URLs

Like Anakin Skywalker turning into Darth Vader, protocol-relative URLs have their quirks in <script> tags:

• IE's Love for Double: Older versions of IE may turn into a Cookie Monster, downloading scripts twice.
• File Protocol: The file:// protocol may falter fetching scripts from Galaxy Far, Far Away (remote server).
• Cross-Domain Scripts: Host your scripts from another domain? Make sure HTTPS is available there, else, face the Sith Lords of security issues.

Solution: Consider bringing the scripts home. Much like Yoda retreating to Dagobah, hosting JavaScript files locally can help with local developments or file:// protocol scenarios.

URI structure and the rebellion of the protocol-relative URLs

According to RFC 3986, a URL structure consists of scheme, authority, path, query, and fragment. You're pulling a Han Solo by ditching the scheme (replacing "http:" with "//") and letting it switch to light-speed (the page's protocol).

• URI or the Death Star's Blueprints: Uniform Resource Identifier structure detailed in RFC 3986.
• Scheme-less Rebellion: Choosing to go rogue by skipping http: or https: in the src attribute of script tag allows these protocol-relative URLs to switch lightsabers (protocols).

Use Cases: Ideal for CDNs, third-party assets, and any resource that needs to swing between HTTP and HTTPS like a Jedi Knight.

Practice your force

While this protocol-relative URL method is like telekinesis in Star Wars Universe, there's always room for caution in the galaxy:

• Train with Yoda (Extensive Testing): Make sure this Padawan is reliable across different protocols and security policies.
• Predictability Is the Way: Beware! The Dark Side of the Force (browser quirks) is strong. Stick to specified protocols for predictable browser behavior.
• Balancing the Force: Evaluate the merits of the Rebel Alliance (convenience) and the Imperial Fleet (potential drawbacks) of using protocol-relative URLs.