talius

Talius

Talius is a parser for CSS selectors. It does not parse CSS, just CSS selectors.

Talius.new accepts a single string as the selector. The Talius object provides an interface with which to access the properties of that selector.

In this example, the selector consists of just a, meaning it selects <a> tags:

raw = 'a'
selector = Talius.new(raw)
rule = selector.rules[0]
rule.tags # => {"a"=>{"name"=>"a"}}

Line 1 creates the raw CSS selector like you might find in a CSS file. Line 2 creates a Talius object.

Each Talius has one or more rules. In this example the object will have one rule. Line 3 gets that rule. Each rule has a hash of tag names in the tags property. Line 4 displays that hash. See below for more about the tags hash.

The following sections will describe how Talius provides information about different elements of a selector. Talius is in its infancy, so there are some important aspects of CSS selectors that it doesn't support. Those aspects are detailed below.

Tags

If a selector contains a tag name, that information will be put into the tags hash of the rule. Consider this example.

raw = 'a'
selector = Talius.new(raw)
rule = selector.rules[0]
rule.tags # => {"a"=>{"name"=>"a"}}
rule.tags['a'].class     # => Talius::Node::Tag
rule.tags['a'].name      # => "a"
rule.tags['a'].namespace # => nil

That selector consists of just a single tag name, so the selector object has just one rule. That rule has a property called tags, which is a hash of the tags in the rule. The key for each hash element is the name of the tag. The value of the element is a Talius::Node::Tag object. That object has two properties, name and namespace.

To indicate the namespace for the tag, put the namespace, followed by |, followed by the name of the tag. For example, the following code has a selector for tags in the mml namespace with the name a. The keys in the tags hash are formatted in the same way.

raw = 'mml|a'
selector = Talius.new(raw)
rule = selector.rules[0]
rule.tags # => {"mml|a"=>{"name"=>"a", "namespace"=>"mml"}}
rule.tags['mml|a'].class     # => Talius::Node::Tag
rule.tags['mml|a'].name      # => "a"
rule.tags['mml|a'].namespace # => "mml"

Multiple rules

For multiple rules for a selector, separate the rules with a comma. For example, the following code parses a selector with two rules, one for the section tag and one for the div tag.

raw = 'section, div'
selector = Talius.new(raw)
selector.rules.length # => 2
selector.rules # => [{"tags"=>{"section"=>{"name"=>"section"}}}, {"tags"=>{"div"=>{"name"=>"div"}}}]

IDs

If any ID descriptions are given, those IDs can be found in the rule's ids hash. The keys are the names of the IDs, the values are always true.

raw = '#overview'
selector = Talius.new(raw)
rule = selector.rules[0]
rule.ids # => {"overview"=>true}

Classes

Classes are available in the classes property of the rule. classes is a simple hash in which the value of each class is true.

raw = 'section.overview.current'
selector = Talius.new(raw)
rule = selector.rules[0]
rule.classes # => {"overview"=>true, "current"=>true}

Attributes

Attribute rules are provided in the rule's atts hash. The hash consists of the key of each attribute and a Talius::Node::Att object.

In this simple example, the selector looks for tags with an rel attribute.

raw = '[rel]'
selector = Talius.new(raw)
rule = selector.rules[0]
att = rule.atts['rel']
att.class # => Talius::Node::Att
att.name  # => rel

If you assign a value to the attribute, that value will be in value property.

raw = '[rel=license]'
selector = Talius.new(raw)
rule = selector.rules[0]
att = rule.atts['rel']
att.name  # => href
att.value # => license

Attribute namespaces are indicated in the same way as with tags. You can access the namespace with the namespace property.

raw = '[mml|rel]'
selector = Talius.new(raw)
rule = selector.rules[0]
att = rule.atts['mml|rel']
att.name      # => rel
att.namespace # => mml

Not implemented

There are a few aspects of CSS selectors that have not yet been implemented.

• Combinators are not parsed.
• The :not() pseudo-class is not understood.

Install

gem install talius

Author

Mike O'Sullivan [e-mail]

Name

"Talius" doesn't mean anything in particular. It just sounded like a good name and it was available on rubygems.rb.

History

version	date	notes
0.5	May 29, 2020	Initial upload.