diff --git a/src/bin/main.rs b/src/bin/main.rs
index 11f308803..92a83dff1 100644
--- a/src/bin/main.rs
+++ b/src/bin/main.rs
@@ -1,9 +1,10 @@
+use std::error::Error;
 use std::fs::{File, read_to_string};
 use std::io::BufWriter;
 use std::path::{Path, PathBuf};
 use futures_executor::block_on;
 
-use typstc::{Typesetter, DynErrorProvider};
+use typstc::{Typesetter, DebugErrorProvider};
 use typstc::toddle::query::fs::EagerFsProvider;
 use typstc::export::pdf;
 
@@ -15,7 +16,7 @@ fn main() {
     }
 }
 
-fn run() -> Result<(), Box<dyn std::error::Error>> {
+fn run() -> Result<(), Box<dyn Error>> {
     let args: Vec<String> = std::env::args().collect();
     if args.len() < 2 || args.len() > 3 {
         println!("usage: {} source [destination]",
@@ -38,7 +39,7 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
         .map_err(|_| "failed to read from source file")?;
 
     let (fs, entries) = EagerFsProvider::from_index("../fonts", "index.json")?;
-    let provider = DynErrorProvider::new(fs);
+    let provider = DebugErrorProvider::new(fs);
     let typesetter = Typesetter::new((Box::new(provider), entries));
 
     let layouts = block_on(typesetter.typeset(&src));
diff --git a/src/error.rs b/src/error.rs
index 1eb48debb..3a095eef3 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -35,3 +35,38 @@ impl Error {
         Error { message: message.into(), severity }
     }
 }
+
+/// Construct an error with formatted message and optionally severity and / or
+/// span.
+///
+/// # Examples
+/// ```
+/// # use typstc::err;
+/// # use typstc::syntax::span::Span;
+/// # let span = Span::ZERO;
+/// # let value = 0;
+///
+/// // With span and default severity `Error`.
+/// err!(span; "the wrong {}", value);
+///
+/// // With no span and severity `Warning`.
+/// err!(@Warning: span; "non-fatal!");
+///
+/// // Without span and default severity.
+/// err!("no spans here ...");
+/// ```
+#[macro_export]
+macro_rules! err {
+    (@$severity:ident: $span:expr; $($args:tt)*) => {
+        $crate::syntax::span::Spanned { v: err!(@$severity: $($args)*), span: $span }
+    };
+
+    (@$severity:ident: $($args:tt)*) => {
+        $crate::error::Error {
+            message: format!($($args)*),
+            severity: $crate::error::Severity::$severity,
+        }
+    };
+
+    ($($tts:tt)*) => { err!(@Error: $($tts)*) };
+}
diff --git a/src/func.rs b/src/func.rs
index 63d7e8efe..590d9ed32 100644
--- a/src/func.rs
+++ b/src/func.rs
@@ -198,38 +198,3 @@ macro_rules! body {
         }
     };
 }
-
-/// Construct an error with formatted message and optionally severity and / or
-/// span.
-///
-/// # Examples
-/// ```
-/// # use typstc::err;
-/// # use typstc::syntax::span::Span;
-/// # let span = Span::ZERO;
-/// # let value = 0;
-///
-/// // With span and default severity `Error`.
-/// err!(span; "the wrong {}", value);
-///
-/// // With no span and severity `Warning`.
-/// err!(@Warning: span; "non-fatal!");
-///
-/// // Without span and default severity.
-/// err!("no spans here ...");
-/// ```
-#[macro_export]
-macro_rules! err {
-    (@$severity:ident: $span:expr; $($args:tt)*) => {
-        $crate::syntax::span::Spanned { v: err!(@Error: $($args)*), span: $span }
-    };
-
-    (@$severity:ident: $($args:tt)*) => {
-        $crate::error::Error {
-            message: format!($($args)*),
-            severity: $crate::error::Severity::$severity,
-        }
-    };
-
-    ($($tts:tt)*) => { err!(@Error: $($tts)*) };
-}
diff --git a/src/lib.rs b/src/lib.rs
index afb327666..2d6fa0216 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -19,7 +19,7 @@
 pub use toddle;
 
 use std::cell::RefCell;
-use std::error::Error;
+use std::fmt::Debug;
 use async_trait::async_trait;
 use smallvec::smallvec;
 
@@ -40,6 +40,7 @@ macro_rules! pub_use_mod {
     };
 }
 
+#[macro_use]
 pub mod error;
 pub mod export;
 #[macro_use]
@@ -71,7 +72,7 @@ pub struct Typesetter {
 pub type GlobalFontLoader = SharedFontLoader<GlobalProvider>;
 
 /// The provider type of font loaders used in the [`Typesetter`].
-pub type GlobalProvider = Box<dyn FontProvider<Data=OwnedData, Error=Box<dyn Error>>>;
+pub type GlobalProvider = Box<dyn FontProvider<Data=OwnedData, Error=Box<dyn Debug>>>;
 
 impl Typesetter {
     /// Create a new typesetter.
@@ -135,29 +136,30 @@ impl Typesetter {
     }
 }
 
-/// Wraps a font provider and transforms its errors into boxed trait objects.
-/// This enables font providers that do not return boxed errors to be used with
-/// the typesetter.
+/// Wraps a font provider and transforms its errors into boxed [`Debug`] trait
+/// objects. This enables font providers that do not return these boxed errors
+/// to be used with the typesetter.
 #[derive(Debug)]
-pub struct DynErrorProvider<P> {
+pub struct DebugErrorProvider<P> {
     provider: P,
 }
 
-impl<P> DynErrorProvider<P>
-where P: FontProvider, P::Error: Error + 'static {
-    /// Create a new dynamic error provider from any provider.
-    pub fn new(provider: P) -> DynErrorProvider<P> {
-        DynErrorProvider { provider }
+impl<P> DebugErrorProvider<P>
+where P: FontProvider, P::Error: Debug + 'static {
+    /// Create a new debug error provider from any provider.
+    pub fn new(provider: P) -> DebugErrorProvider<P> {
+        DebugErrorProvider { provider }
     }
 }
 
 #[async_trait(?Send)]
-impl<P> FontProvider for DynErrorProvider<P>
-where P: FontProvider, P::Error: Error + 'static {
+impl<P> FontProvider for DebugErrorProvider<P>
+where P: FontProvider, P::Error: Debug + 'static {
     type Data = P::Data;
-    type Error = Box<dyn Error>;
+    type Error = Box<dyn Debug>;
 
     async fn load(&self, index: usize, variant: usize) -> Result<Font<P::Data>, Self::Error> {
-        Ok(self.provider.load(index, variant).await?)
+        self.provider.load(index, variant).await
+            .map_err(|d| Box::new(d) as Box<dyn Debug>)
     }
 }
diff --git a/src/library/font.rs b/src/library/font.rs
index be4d263ff..422a68f97 100644
--- a/src/library/font.rs
+++ b/src/library/font.rs
@@ -15,7 +15,7 @@ function! {
         FontFamilyFunc {
             body: body!(opt: body, ctx, errors, decos),
             list: header.args.pos.get_all::<StringLike>(errors)
-                .map(Into::into)
+                .map(|s| s.0.to_lowercase())
                 .collect(),
         }
     }
diff --git a/src/syntax/func/keys.rs b/src/syntax/func/keys.rs
index cb12ee1b5..b8f142eed 100644
--- a/src/syntax/func/keys.rs
+++ b/src/syntax/func/keys.rs
@@ -105,7 +105,7 @@ key!(AxisKey,
 /// A key which is equivalent to a [`AxisKey`] but uses typical extent keywords
 /// instead of axis keywords, e.g. `width` instead of `horizontal`.
 #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
-pub struct ExtentKey(AxisKey);
+pub struct ExtentKey(pub AxisKey);
 
 key!(ExtentKey,
     "width"          | "w"  => ExtentKey(Specific(Horizontal)),
diff --git a/src/syntax/func/values.rs b/src/syntax/func/values.rs
index 18d451e3f..d2b54a0b7 100644
--- a/src/syntax/func/values.rs
+++ b/src/syntax/func/values.rs
@@ -87,7 +87,7 @@ value!(ScaleSize, "number or size",
 
 /// A value type that matches [`Expr::Ident`] and [`Expr::Str`] and implements
 /// `Into<String>`.
-pub struct StringLike(String);
+pub struct StringLike(pub String);
 
 value!(StringLike, "identifier or string",
     Expr::Ident(Ident(s)) => StringLike(s),
@@ -117,7 +117,7 @@ impl From<StringLike> for String {
 /// [func: size=default] => None
 /// [func: size=2cm]     => Some(Size::cm(2.0))
 /// ```
-pub struct Defaultable<V>(Option<V>);
+pub struct Defaultable<V>(pub Option<V>);
 
 impl<V: Value> Value for Defaultable<V> {
     fn parse(expr: Spanned<Expr>) -> Result<Self, Error> {
diff --git a/tests/src/typeset.rs b/tests/src/typeset.rs
index 6a5cdb9e5..61889e956 100644
--- a/tests/src/typeset.rs
+++ b/tests/src/typeset.rs
@@ -8,7 +8,7 @@ use std::process::Command;
 
 use futures_executor::block_on;
 
-use typstc::{Typesetter, DynErrorProvider};
+use typstc::{Typesetter, DebugErrorProvider};
 use typstc::layout::{MultiLayout, Serialize};
 use typstc::size::{Size, Size2D, ValueBox};
 use typstc::style::{PageStyle, PaperClass};
@@ -65,8 +65,8 @@ fn test(name: &str, src: &str) -> DynResult<()> {
     println!("Testing: {}.", name);
 
     let (fs, entries) = EagerFsProvider::from_index("../fonts", "index.json")?;
-    let paths = fs.paths();
-    let provider = DynErrorProvider::new(fs);
+    let files = fs.files().to_vec();
+    let provider = DebugErrorProvider::new(fs);
     let mut typesetter = Typesetter::new((Box::new(provider), entries));
 
     typesetter.set_page_style(PageStyle {
@@ -84,14 +84,12 @@ fn test(name: &str, src: &str) -> DynResult<()> {
 
     // Compute the font's paths.
     let mut fonts = HashMap::new();
-    let loader = typesetter.loader().borrow();
     for layout in &layouts {
         for index in layout.find_used_fonts() {
             fonts.entry(index)
-                .or_insert_with(|| &paths[index.id][index.variant]);
+                .or_insert_with(|| &files[index.id][index.variant]);
         }
     }
-    drop(loader);
 
     // Write the serialized layout file.
     let path = format!("tests/cache/{}.serialized", name);