Flesh out ActiveStorage::Filename docs

activestorage/app/models/active_storage/filename.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
-# Encapsulates a string representing a filename to provide convenience access to parts of it and a sanitized version.
-# This is what's returned by ActiveStorage::Blob#filename. A Filename instance is comparable so it can be used for sorting.
+# Encapsulates a string representing a filename to provide convenient access to parts of it sanitization.
+# A Filename instance is returned by ActiveStorage::Blob#filename, and is comparable so it can be used for sorting.
 class ActiveStorage::Filename
   include Comparable
 
@@ -9,23 +9,31 @@ class ActiveStorage::Filename
     @filename = filename
   end
 
-  # Returns the basename of the filename.
+  # Returns the part of the filename preceding any extension.
   #
   #   ActiveStorage::Filename.new("racecar.jpg").base # => "racecar"
+  #   ActiveStorage::Filename.new("racecar").base     # => "racecar"
+  #   ActiveStorage::Filename.new(".gitignore").base  # => ".gitignore"
   def base
     File.basename @filename, extension_with_delimiter
   end
 
-  # Returns the extension with delimiter of the filename.
+  # Returns the extension of the filename (i.e. the substring following the last dot, excluding a dot at the
+  # beginning) with the dot that precedes it. If the filename has no extension, an empty string is returned.
   #
   #   ActiveStorage::Filename.new("racecar.jpg").extension_with_delimiter # => ".jpg"
+  #   ActiveStorage::Filename.new("racecar").extension_with_delimiter     # => ""
+  #   ActiveStorage::Filename.new(".gitignore").extension_with_delimiter  # => ""
   def extension_with_delimiter
     File.extname @filename
   end
 
-  # Returns the extension without delimiter of the filename.
+  # Returns the extension of the filename (i.e. the substring following the last dot, excluding a dot at
+  # the beginning). If the filename has no extension, an empty string is returned.
   #
   #   ActiveStorage::Filename.new("racecar.jpg").extension_without_delimiter # => "jpg"
+  #   ActiveStorage::Filename.new("racecar").extension_without_delimiter     # => ""
+  #   ActiveStorage::Filename.new(".gitignore").extension_without_delimiter  # => ""
   def extension_without_delimiter
     extension_with_delimiter.from(1).to_s
   end
@@ -37,7 +45,7 @@ class ActiveStorage::Filename
   #   ActiveStorage::Filename.new("foo:bar.jpg").sanitized # => "foo-bar.jpg"
   #   ActiveStorage::Filename.new("foo/bar.jpg").sanitized # => "foo-bar.jpg"
   #
-  # ...and any other character unsafe for URLs or storage is converted or stripped.
+  # Characters considered unsafe for storage (e.g. \, $, and the RTL override character) are replaced with a dash.
   def sanitized
     @filename.encode(Encoding::UTF_8, invalid: :replace, undef: :replace, replace: "<EFBFBD>").strip.tr("\u{202E}%$|:;/\t\r\n\\", "-")
   end