Please Whitelist This Site? I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :) If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads. If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK. Thanks for your understanding! Sincerely, Charles Kozierok Author and Publisher, The TCP/IP Guide

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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Key Applications and Application Protocols            9  TCP/IP Application Layer Addressing: Uniform Resource Identifiers, Locators and Names (URIs, URLs and URNs)                 9  Uniform Resource Locators (URLs)

URL Relative Syntax and Base URLs 1 2 3 4 URL Obscuration, Obfuscation and General Trickery

URL Wrapping and Delimiting Issues

For humans, long and complex URLs are hard to remember and use. In addition to the sheer difficulty of remembering all those characters, there is the issue of URL wrapping, which occurs when they are presented in certain forms. Most programs can only display 78 or 80 characters in a single line. If a URL is longer than this, the characters of the URL will “wrap” onto multiple lines; when you read that Google example just above, you probably noticed that.

URL wrapping can lead to mistakes when copying a URL from one form to another, such as if you copied it from this document into your Web browser. If a URL is 81 characters long and 80 are on the first line and the last character on the second line, many users may not realize that the URL has “wrapped” at all. I have seen URLs that are hundreds of characters long, requiring several manual “copy and paste” operations to get the URL to work.

Perhaps surprisingly, some software may not handle this “wrapping” properly either. While this is not a problem when a hyperlink is used in something like an HTML document, it can be troublesome when links are included in an e-mail message or Usenet article.

Another issue is delimiting where a URL starts and ends when it appears. A URL begins with a scheme name that could in theory be used in other contexts that are not URLs. Without a clear way of labeling a URL as being a URL, a software program might not recognize it. Consider discussion of a URL in a document like this one; if I say “Please visit http://www.thissite.com; you will see the information you need there”, then we all know the semicolon is part of the sentence and not part of the URL, but a computer program might not be so sure. And again, this problem is worse when a URL is long and complex and wraps on to multiple lines of textfl—how does the program recognize the end of the URL?

URL Relative Syntax and Base URLs 1 2 3 4 URL Obscuration, Obfuscation and General Trickery