URLs consist of letters, numbers, and punctuation.

   The basic structure of a URL is hierarchical, and the
   hierarchy moves from left to right:

protocol://server-name.domain-name.top-level-domain:port/directory/filename

Examples:

http://www.healthyway.com:8080/exercise/mtbike.html
gopher://gopher.state.edu/
ftp://ftp.company.com/


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