CSS to XPath

Converts most CSS 2.1/3 selectors (see exclusions below) to equivalent XPath 1.0 expression.

See test.js for examples.

Extension pseudos

To take advantage of the different capabilities of XPath some additional pseudo selectors have been implemented:

#### :text

All text matching pseudo classes normalize whitespace and ignore tags.
E.g. " my string " is treated as "my string".

* :text("foo") Case-insensitive matching of element text
* :text-case("foo") Case-sensitive :text-case
* :text-contains("foo") Case-insensitive substring matching of element text
* :text-contains-case("foo") Case-sensitive :text-contains
* :text-start("foo") Case-insensitive matching of element starting text
* :text-start-case("foo") Case-sensitive :text-start
* :text-end("foo") Case-insensitive matching of element ending text
* :text-end-case("foo") Case-sensitive :text-end

#### :any

Selectors containing multiple options, any one of which will be matched:

E.g: div :any(ol, ul, dl) > equates to div ol > , div ul > , div dl >

#### :comment

* :comment Select comment nodes
* :comment(n) Select comment nodes at child position n

Note: Can be combined with :text to match based on comment text content. E.g. p > :comment:text("foo")

#### :childless

As :empty but ignoring whitespace.

Aliased pseudos

* :first is aliased to :first-child
* :last is aliased to :last-child
* :child is aliased to :nth-child
* :contains is aliased to :text-contains

Author pseudos

Authored pseudos can serve as aliases to help simplify selector chains:

``js
/*
* If the pseudos option is set the CSS expression is
* preprocessed before generating the XPath expression:
*
* :radio
* => input[type="radio"]
*
* :element-1(Hello)
* => element:child(1):contains("Hello")
*/
const cssToXpath = require('csstoxpath');
const xpathExpr = cssToXpath(':radio, :element-1(Hello)', {
pseudos: {
radio: 'input[type="radio"]',
[/element-(\d+)/]: (data, m) => element:child(${m[1]}):contains("${data}"),
}
});
`

Limitations

The following pseudos are partially supported as they require a tag context:

* :nth-of-type
* :first-of-type
* :last-of-type

The following pseudos are currently unsupported:

* :nth-last-child
* :nth-last-of-type

Dynamic pseudos are excluded as they can only be partially supported by attribute matching:

* :checked
* :disabled
* :enabled
* :required
* :lang

The following cannot be implemented in XPath 1.0:

* States: :hover, :focus, :active, :visited, :target etc.
* Elements: ::before, ::after, ::first-letter` etc.