[Sass] Document a few undocumented methods.

lib/sass/selector.rb

@@ -308,6 +308,10 @@ module Sass
         res
       end
 
+      # Returns `nil` if this is a pseudoclass selector
+      # and `sels` contains a pseudoclass selector different than this one.
+      #
+      # @see Selector#unify
       def unify(sels)
         return if type == :element && sels.any? do |sel|
           sel.is_a?(Pseudo) && sel.type == :element &&

lib/sass/tree/extend_node.rb

@@ -1,12 +1,23 @@
 require 'sass/tree/node'
 
 module Sass::Tree
+  # A static node reprenting an `@extend` directive.
+  #
+  # @see Sass::Tree
   class ExtendNode < Node
+    # @param selector [Array<String, Sass::Script::Node>]
+    #   The CSS selector to extend,
+    #   interspersed with {Sass::Script::Node}s
+    #   representing `#{}`-interpolation.
     def initialize(selector)
       @selector = selector
       super()
     end
 
+    # Registers this extension in the `extends` subset map.
+    #
+    # @param parent [RuleNode] The parent node of this node
+    # @see Node#cssize
     def cssize(extends, parent)
       @resolved_selector.members.each do |seq|
         if seq.members.size > 1
@@ -33,6 +44,11 @@ module Sass::Tree
 
     protected
 
+    # Runs SassScript interpolation in the selector,
+    # and then parses the result into a {Sass::Selector::CommaSequence}.
+    #
+    # @param environment [Sass::Environment] The lexical environment containing
+    #   variable and mixin values
     def perform!(environment)
       @resolved_selector = Sass::SCSS::CssParser.new(run_interp(@selector, environment)).
         parse_selector(self.line, self.filename)

lib/sass/tree/rule_node.rb

@@ -185,8 +185,8 @@ module Sass::Tree
       to_return
     end
 
-    # Runs any SassScript that may be embedded in the rule,
-    # and parses the selectors for commas.
+    # Runs SassScript interpolation in the selector,
+    # and then parses the result into a {Sass::Selector::CommaSequence}.
     #
     # @param environment [Sass::Environment] The lexical environment containing
     #   variable and mixin values