simple_selector

simple_selector is a Ruby gem that represents a CSS-like selector, calculates its specificity and tells if it matches given HTML-like tags.

Content

The selector content can consist of tag names, IDs and class names. An example:

  SimpleSelector.new("tag_a#id_a.class_a #id_b .class_c.class_d")

Specificity

Calculation rules

The specificity of a selector is calculated according to rules similar to the standard CSS rules.

The specificity is four numbers: a,b,c,d.

The rules respected by this gem are:

• a is always 0;
• b is the number of ID attributes in the selector;
• c is the number of class names in the selector;
• d is the number of tag names in the selector.

For example, a selector tag#id1.class1 #id2.class2.class3 has specificity equal to 0,2,3,1.

  SimpleSelector.new("tag#id1.class1 #id2.class2.class3").specificity
   => #<SimpleSelector::Specificity "0,2,3,1">

Comparison

Specificity allows selector comparison.

Two selector specificities are compared by succesively comparing their corresponding numbers, from left to right.

Tag matching

A SimpleSelector object tells if it matches given HTML-like tags.

The tag is expected to be represented by an object which responds to :name, :id, :class_names and :parent messages. An example:

  Tag = Struct.new(:name, :id, :class_names, :parent)

  # Tag objects corresponding to the structure:
  # <section id="content"><message class="success">...</message></section>
  content_tag = Tag.new("section", "content", [], nil)
  message_tag = Tag.new("message", nil, ["success"], content_tag)

And now:

  SimpleSelector.new("section#content message.success").match?(message_tag)
   => true

Installation

As a Ruby gem, simple_selector can be installed either by running

  gem install simple_selector

or adding

  gem "simple_selector"

to the Gemfile and then invoking bundle install.

License

License is included in the LICENSE file.