better Scribble support for disabling line breaks

- make 'no-break element style work consistently
 - document 'no-break
 - add `nonbreaking' to `scribble/base'

original commit: 315fdf071a2905ff4d634c7b8004e32c0d6a1b58

collects/scribble/base.rkt

@@ -276,6 +276,7 @@
 
 (provide/contract
  [linebreak (-> element?)]
+ [nonbreaking elem-like-contract]
  [hspace (-> exact-nonnegative-integer? element?)]
  [elem (->* ()
             (#:style element-style?)
@@ -311,6 +312,9 @@
 (define (linebreak)
   (make-element 'newline '("\n")))
 
+(define (nonbreaking . str)
+  (make-element 'no-break (decode-content str)))
+
 (define (elem #:style [style plain] . str)
   (make-element style (decode-content str)))
 

collects/scribble/latex-render.rkt

@@ -272,7 +272,7 @@
                   [(bold) (wrap e "textbf" tt?)]
                   [(tt) (wrap e "Scribtexttt" #t)]
                   [(url) (wrap e "nolinkurl" 'exact)]
-                  [(no-break) (core-render e tt?)]
+                  [(no-break) (wrap e "mbox" tt?)]
                   [(sf) (wrap e "textsf" #f)]
                   [(subscript) (wrap e "textsub" #f)]
                   [(superscript) (wrap e "textsuper" #f)]

collects/scribblings/scribble/base.scrbl

@@ -346,6 +346,10 @@ See also @racket[verbatim].}
 Produces an element that forces a line break.}
 
 
+@def-elem-proc[nonbreaking]{Like @racket[elem], but line breaks are
+suppressed while rendering the content.}
+
+
 @defproc[(hspace [n exact-nonnegative-integer?]) element?]{
 
 Produces an element containing @racket[n] spaces and style

collects/scribblings/scribble/core.scrbl

@@ -646,6 +646,9 @@ recognized:
  @item{@racket['newline] --- Renders a line break independent of
        the @racket[content].}
 
+ @item{@racket['no-break] --- Prevents line breaks when rendering
+       @racket[content].}
+
 ]
 
 The following @tech{style properties} are currently recognized: