[Ur] Defining new tags like <pre>...

[Michael Stone]

Dear Adam, and other ur@ folks,

First, thanks very much for publishing this fascinating language.

Second, in the course of playing with Ur/Web over the last few hours,
I encountered a need to produce an HTML <pre> tag in a page.

I was able to accomplish this objective by adding an entry to
lib/ur/basis.urs like so:

  val div : bodyTag boxAttrs
  val span : bodyTag boxAttrs
+  val pre : bodyTag boxAttrs

Unfortunately, I don't fully understand why making this change has the
desired effect. Would you mind saying a few words about why defining
this value "just works"?

Regards,

Michael