[librsvg] Doc comments for the Parse trait

[Federico Mena Quintero <federico src gnome org>]

commit f6cf1eb53c922d4c7cc3235bef2e21bc3a8c86e5
Author: Federico Mena Quintero <federico gnome org>
Date:   Wed Dec 4 16:22:15 2019 -0600

    Doc comments for the Parse trait

 rsvg_internals/src/parsers.rs         | 11 +++++++++++
 rsvg_internals/src/property_macros.rs |  4 ++--
 2 files changed, 13 insertions(+), 2 deletions(-)
---
diff --git a/rsvg_internals/src/parsers.rs b/rsvg_internals/src/parsers.rs
index 2d305930..f107bc0a 100644
--- a/rsvg_internals/src/parsers.rs
+++ b/rsvg_internals/src/parsers.rs
@@ -24,11 +24,20 @@ impl<'a> From<BasicParseError<'a>> for ParseError {
     }
 }
 
+/// Trait to parse values using `cssparser::Parser`.
 pub trait Parse: Sized {
+    /// Error type for parse errors.
     type Err;
 
+    /// Parses a value out of the `parser`.
+    ///
+    /// All value types should implement this for composability.
     fn parse(parser: &mut Parser<'_, '_>) -> Result<Self, Self::Err>;
 
+    /// Convenience function to parse a value out of a `&str`.
+    ///
+    /// This is useful mostly for tests which want to avoid creating a
+    /// `cssparser::Parser` by hand.
     fn parse_str(s: &str) -> Result<Self, Self::Err> {
         let mut input = ParserInput::new(s);
         let mut parser = Parser::new(&mut input);
@@ -40,10 +49,12 @@ pub trait Parse: Sized {
     }
 }
 
+/// Extra utility methods for `cssparser::Parser`.
 pub trait CssParserExt {
     /// Avoid infinities.
     fn expect_finite_number(&mut self) -> Result<f32, ValueErrorKind>;
 
+    /// Consumes a comma if it exists, or does nothing.
     fn optional_comma(&mut self);
 }
 
diff --git a/rsvg_internals/src/property_macros.rs b/rsvg_internals/src/property_macros.rs
index 7908d368..547fd069 100644
--- a/rsvg_internals/src/property_macros.rs
+++ b/rsvg_internals/src/property_macros.rs
@@ -24,8 +24,8 @@ pub trait Property<T> {
 /// The macro will generate a `StrokeLinejoin` enum with the provided
 /// variants.  It will generate an `impl Default for StrokeLinejoin`
 /// with the provided `default:` value.  Finally, it will generate an
-/// `impl Parse for StrokeLinejoin`, from `parsers::Parse`, where
-/// `type Data = ()` and `type Err = ValueErrorKind`.
+/// `impl Parse for StrokeLinejoin`, from `parsers::Parse`, with
+/// `type Err = ValueErrorKind`.
 #[macro_export]
 macro_rules! make_property {
     ($computed_values_type: ty,