If you put a URL into the body of a node, one of Drupal's input filters will automatically turn that URL into a clickable web link, like this: http://www.youtube.com/watch?v=Fc9B2g_1h1o
You can also use a special "markdown" shortcut for making links; this is better for referring to other pages on CNMAT's Drupal site.
For example, to link to [http://www.ircam.fr/sdif|IRCAM's SDIF web pages], put this in the text of your body:
To link to a page on this same site, for example [cnmat:node/2588|a link to this page], use the "cnmat:" abbreviation, like this:
[cnmat:node/2588|a link to this page]
Notice there is no "/" before "node/2588" - this mechanism will break if you include a leading slash.
Other useful link abbreviations, include those for Wikipedia and for Julius Smith's web pages:
[w:CNMAT|the Wikipedia article on CNMAT]
[jos: minimum-phase filter|Julius Smith's page(s) on minimum-phase filters]
This list will evolve as we find ourselves repeatedly referring to the same sites. Consult
[cnmat:interwiki/6|the entire list of link abbreviations] from the confusingly misnamed "Wiki filter prefixes" module for more details.
Non-volatile URLs
Books and categories have automatically-generated URL aliases based on the title and all the titles of all the parent nodes, not including common words like "of", "the", etc. For example, at the time that I'm writing this node, its URL is [cnmat:library/cnmat_users_manual/website_handbook/how_guides/how_add_link_body_node|/library/cnmat_users_manual/website_handbook/how_guides/how_add_link_body_node]. If any of these titles change then the URL of one or mode nodes will change and the link in this paragraph will break.
To create a reliable link to a node whose title might change you can use a URL that references the node by its number which will never change. In this case the node number if 2588, so a link like [cnmat:node/2588|this] (which you'd write like [cnmat:node/2588 |this] in the body of your node) will always point to this page.
[cnmat:case/2499|Some day we might install a Drupal "input filter" that automatically converts volatile symbolic URLs into permanent node numbers.] Then you won't have to worry about this.