[NTG-context] What is the third parameter in \useURL for?

For \useURL the first parameter identifies the statement, the second defines the url, the third is usually blank and the fourth gives the text to appear in the clickable area. What is that third parameter for? -- John Culleton Books with answers to marketing and publishing questions: http://wexfordpress.com/tex/shortlist.pdf Book coaches, consultants and packagers: http://wexfordpress.com/tex/packagers.pdf