diff --git a/lib/linguist/shebang.rb b/lib/linguist/shebang.rb
index 290dca70..7d1c0e8c 100644
--- a/lib/linguist/shebang.rb
+++ b/lib/linguist/shebang.rb
@@ -3,17 +3,20 @@ module Linguist
     # Public: Use shebang to detect language of the blob.
     #
     # blob               - An object that quacks like a blob.
+    # candidates         - A list of candidate languages.
     #
     # Examples
     #
     #   Shebang.call(FileBlob.new("path/to/file"))
     #
-    # Returns an Array with one Language if the blob has a shebang with a valid
-    # interpreter, or empty if there is no shebang.
-    def self.call(blob, _ = nil)
+    # Returns an array of languages from the candidate list for which the
+    # blob's shebang is valid. Returns an empty list if there is no shebang.
+    # If the candidate list is empty, any language is a valid candidate.
+    def self.call(blob, candidates)
       return [] if blob.symlink?
 
-      Language.find_by_interpreter interpreter(blob.data)
+      languages = Language.find_by_interpreter interpreter(blob.data)
+      candidates.any? ? candidates & languages : languages
     end
 
     # Public: Get the interpreter from the shebang
diff --git a/lib/linguist/strategy/extension.rb b/lib/linguist/strategy/extension.rb
index 161dc34c..b5dd6e9f 100644
--- a/lib/linguist/strategy/extension.rb
+++ b/lib/linguist/strategy/extension.rb
@@ -2,8 +2,21 @@ module Linguist
   module Strategy
     # Detects language based on extension
     class Extension
-      def self.call(blob, _)
-        Language.find_by_extension(blob.name.to_s)
+      # Public: Use the file extension to detect the blob's language.
+      #
+      # blob               - An object that quacks like a blob.
+      # candidates         - A list of candidate languages.
+      #
+      # Examples
+      #
+      #   Extension.call(FileBlob.new("path/to/file"))
+      #
+      # Returns an array of languages associated with a blob's file extension.
+      # Selected languages must be in the candidate list, except if it's empty,
+      # in which case any language is a valid candidate.
+      def self.call(blob, candidates)
+        languages = Language.find_by_extension(blob.name.to_s)
+        candidates.any? ? candidates & languages : languages
       end
     end
   end
diff --git a/lib/linguist/strategy/filename.rb b/lib/linguist/strategy/filename.rb
index f3656515..39b9ff1b 100644
--- a/lib/linguist/strategy/filename.rb
+++ b/lib/linguist/strategy/filename.rb
@@ -2,9 +2,22 @@ module Linguist
   module Strategy
     # Detects language based on filename
     class Filename
-      def self.call(blob, _)
+      # Public: Use the filename to detect the blob's language.
+      #
+      # blob               - An object that quacks like a blob.
+      # candidates         - A list of candidate languages.
+      #
+      # Examples
+      #
+      #   Filename.call(FileBlob.new("path/to/file"))
+      #
+      # Returns an array of languages with a associated blob's filename.
+      # Selected languages must be in the candidate list, except if it's empty,
+      # in which case any language is a valid candidate.
+      def self.call(blob, candidates)
         name = blob.name.to_s
-        Language.find_by_filename(name)
+        languages = Language.find_by_filename(name)
+        candidates.any? ? candidates & languages : languages
       end
     end
   end
diff --git a/test/fixtures/Perl/01-methods.pl b/test/fixtures/Perl/01-methods.pl
new file mode 100644
index 00000000..251bd4b0
--- /dev/null
+++ b/test/fixtures/Perl/01-methods.pl
@@ -0,0 +1,51 @@
+#!perl
+use Test::More;
+use Test::Exception;
+
+use_ok 'Music::ScaleNote';
+
+my $msn = Music::ScaleNote->new(
+    scale_note => 'C',
+    scale_name => 'pminor',
+#    verbose    => 1,
+);
+isa_ok $msn, 'Music::ScaleNote';
+
+my $x;
+
+throws_ok { $x = $msn->get_offset() }
+    qr/note_name, note_format or offset not provided/, 'invalid get_offset';
+
+my $format = 'midinum';
+$x = $msn->get_offset(
+    note_name   => 60,
+    note_format => $format,
+    offset      => 1,
+);
+is $x->format($format), 63, 'get_offset';
+
+$format = 'ISO';
+$x = $msn->get_offset(
+    note_name   => 'D#4',
+    note_format => $format,
+    offset      => -1,
+);
+is $x->format($format), 'C4', 'get_offset';
+
+throws_ok {
+    $x = $msn->get_offset(
+        note_name   => 'C0',
+        note_format => $format,
+        offset      => -1,
+    )
+} qr/Octave: -1 out of bounds/, 'out of bounds';
+
+throws_ok {
+    $x = $msn->get_offset(
+        note_name   => 'A#127',
+        note_format => $format,
+        offset      => 1,
+    )
+} qr/Octave: 128 out of bounds/, 'out of bounds';
+
+done_testing();