[librsvg] space.rs: Include the relevant portions of the spec

[Federico Mena Quintero <federico src gnome org>]

commit 7a113a9eb366fc4b5ec395a21380f57961388459
Author: Federico Mena Quintero <federico gnome org>
Date:   Thu Dec 7 09:28:07 2017 -0600

    space.rs: Include the relevant portions of the spec

 rust/src/space.rs |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)
---
diff --git a/rust/src/space.rs b/rust/src/space.rs
index 48531c0..56f7d2e 100644
--- a/rust/src/space.rs
+++ b/rust/src/space.rs
@@ -16,6 +16,14 @@ pub fn xml_space_normalize(mode: XmlSpace, s: &str) -> String {
     }
 }
 
+// From https://www.w3.org/TR/SVG/text.html#WhiteSpace
+//
+// When xml:space="default", the SVG user agent will do the following
+// using a copy of the original character data content. First, it will
+// remove all newline characters. Then it will convert all tab
+// characters into space characters. Then, it will strip off all
+// leading and trailing space characters. Then, all contiguous space
+// characters will be consolidated.
 fn normalize_default(s: &str) -> String {
     #[derive(PartialEq)]
     enum State {
@@ -52,6 +60,16 @@ fn normalize_default(s: &str) -> String {
     result
 }
 
+// From https://www.w3.org/TR/SVG/text.html#WhiteSpace
+//
+// When xml:space="preserve", the SVG user agent will do the following
+// using a copy of the original character data content. It will
+// convert all newline and tab characters into space characters. Then,
+// it will draw all space characters, including leading, trailing and
+// multiple contiguous space characters. Thus, when drawn with
+// xml:space="preserve", the string "a   b" (three spaces between "a"
+// and "b") will produce a larger separation between "a" and "b" than
+// "a b" (one space between "a" and "b").
 fn normalize_preserve(s: &str) -> String {
     s.chars()
         .map(|ch| {