After you do so, you will then see Develop on Safari's menu bar. If you click on it, you will see a Show Page Source option.
The develop menu also provides a User Agent option that will allow you to change the user agent Safari reports to web sites.
Some websites, instead of relying on Internet standards, will check to see what browser a visitor is using and will refuse to display some or any content if the site doesn't approve of the browser the user is using. Browsers send a "user agent" parameter to websites allowing websites to identify the browser. Spoofing the user agent Safari reports to the website may allow content to be accessed that couldn't be viewed otherwise.
Choices offered by Safari 6.2.7 (85184.108.40.206) on Mac OS X for the user agent string it sends include the following:
Selecting "Other" allows you to specify a custom user agent of your choosing.