keyword procedures?

[Thomas Bushnell, BSG]

The guile manual suggests that Guile has support keyword arguments,
but contains no information beyond a chapter heading.

But it looks like it's in ice-9/optarg.scm.  So some questions:

  *Exactly* when are default expressions evaluated, and with what
  bindings already made?

  I need to generate keywords programmatically.  What is the analog of
  string->symbol for keywords, and can you give an example of its use?

  Is lambda* more widely implemented than just in Guile?

Thomas