The first parameter is parsed to see if it takes the form of a complete URL. If it doesn't start with a URI scheme (such as "http:", "https:", or "ftp:"), an "http://" prefix will be prepended to the specified generated target URL of the link.
If no display text is specified or is empty, a default display text will be inferred by trying to reduce the specified URL without its URI scheme (and without the default "/" path), and the domain name part will be forced to lowercase (for shorter and canonical display, but also to limit the occurrences of easily confusable characters, for example between letters and digits). The rest of the URL (including the path, the query string and the fragment identifier) will be displayed unchanged.
The url or domain name is optional : if it is not specified in the first parameter or this parameter is empty, the display text becomes mandatory, and will be displayed without any change.
If both parameters are missing or empty, a default message referencing a correct usage of this template will be generated (including a link to this page), to help editors.
The parameters must be numbered explicitly if the URL contains an equal sign, as is common in the query string. This applies when the value of the URL is unknown, for example when this template is used in another template specifying the effective URL as a variable value. The second parameter for the displayed text, if present, must also be explicitly numbered if the first parameter is explicitly numbered; otherwise it will override the value of the first parameter.