diff --git a/lib/linguist/mime.rb b/lib/linguist/mime.rb
index 8311f6ed..2daf4f80 100644
--- a/lib/linguist/mime.rb
+++ b/lib/linguist/mime.rb
@@ -2,7 +2,8 @@ require 'mime/types'
 require 'yaml'
 
 # Register additional mime type extensions
-YAML.load_file(File.expand_path("../mimes.yml", __FILE__)).each do |mime_type, exts|
+mime_extensions = YAML.load_file(File.expand_path("../mimes.yml", __FILE__))
+mime_extensions.each do |mime_type, exts|
   mime = MIME::Types[mime_type].first
   exts.each { |ext| mime.extensions << ext }
   MIME::Types.index_extensions(mime)
@@ -10,19 +11,52 @@ end
 
 module Linguist
   module Mime
-    Special = YAML.load_file(File.expand_path("../content_types.yml", __FILE__))
-
+    # Internal: Look up mime type for extension.
+    #
+    # ext - The extension String. May include leading "."
+    #
+    # Examples
+    #
+    #   Mime.mime_for('.html')
+    #   # => 'text/html'
+    #
+    #   Mime.mime_for('txt')
+    #   # => 'text/plain'
+    #
+    # Return mime type String otherwise falls back to 'text/plain'.
     def self.mime_for(ext)
       ext ||= ''
       guesses = ::MIME::Types.type_for(ext)
       guesses.first ? guesses.first.simplified : 'text/plain'
     end
 
+    Special = YAML.load_file(File.expand_path("../content_types.yml", __FILE__))
+
+    # Internal: Look up Content-Type header to serve for extension.
+    #
+    # This value is used when serving raw blobs.
+    #
+    #   /github/linguist/raw/master/lib/linguist/mime.rb
+    #
+    # ext - The extension String. May include leading "."
+    #
+    #   Mime.content_type_for('.html')
+    #   # => 'text/plain; charset=utf-8'
+    #
+    # Return Content-Type String otherwise falls back to
+    # 'text/plain; charset=utf-8'.
     def self.content_type_for(ext)
       ext ||= ''
+
+      # Lookup mime type
       type = mime_for(ext)
+
+      # Substitute actual mime type if an override exists in content_types.yml
       type = Special[type] || Special[ext.sub(/^\./, '')] || type
+
+      # Append default charset to text files
       type += '; charset=utf-8' if type =~ /^text\//
+
       type
     end
   end