XPath
====
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XPath is Go package provides selecting nodes from XML, HTML or other documents using XPath expression.

Implementation
===

- [htmlquery](https://github.com/antchfx/htmlquery) - an XPath query package for HTML document

- [xmlquery](https://github.com/antchfx/xmlquery) - an XPath query package for XML document.

- [jsonquery](https://github.com/antchfx/jsonquery) - an XPath query package for JSON document

Supported Features
===

#### The basic XPath patterns.

> The basic XPath patterns cover 90% of the cases that most stylesheets will need.

- `node` : Selects all child elements with nodeName of node.

- `*` : Selects all child elements.

- `@attr` : Selects the attribute attr.

- `@*` : Selects all attributes.

- `node()` : Matches an org.w3c.dom.Node.

- `text()` : Matches a org.w3c.dom.Text node.

- `comment()` : Matches a comment.

- `.` : Selects the current node.

- `..` : Selects the parent of current node.

- `/` : Selects the document node.

- `a[expr]` : Select only those nodes matching a which also satisfy the expression expr.

- `a[n]` : Selects the nth matching node matching a When a filter's expression is a number, XPath selects based on position.

- `a/b` : For each node matching a, add the nodes matching b to the result.

- `a//b` : For each node matching a, add the descendant nodes matching b to the result. 

- `//b` : Returns elements in the entire document matching b.

- `a|b` : All nodes matching a or b, union operation(not boolean or).

#### Node Axes 

- `child::*` : The child axis selects children of the current node.

- `descendant::*` : The descendant axis selects descendants of the current node. It is equivalent to '//'.

- `descendant-or-self::*` : Selects descendants including the current node.

- `attribute::*` : Selects attributes of the current element. It is equivalent to @*

- `following-sibling::*` : Selects nodes after the current node.

- `preceding-sibling::*` : Selects nodes before the current node.

- `following::*` : Selects the first matching node following in document order, excluding descendants. 

- `preceding::*` : Selects the first matching node preceding in document order, excluding ancestors. 

- `parent::*` : Selects the parent if it matches. The '..' pattern from the core is equivalent to 'parent::node()'.

- `ancestor::*` : Selects matching ancestors.

- `ancestor-or-self::*` : Selects ancestors including the current node.

- `self::*` : Selects the current node. '.' is equivalent to 'self::node()'.

#### Expressions

 The gxpath supported three types: number, boolean, string.

- `path` : Selects nodes based on the path.

- `a = b` : Standard comparisons.

    * a = b	    True if a equals b.
    * a != b	True if a is not equal to b.
    * a < b	    True if a is less than b.
    * a <= b	True if a is less than or equal to b.
    * a > b	    True if a is greater than b.
    * a >= b	True if a is greater than or equal to b.

- `a + b` : Arithmetic expressions.

    * `- a`	Unary minus
    * a + b	Add
    * a - b	Substract
    * a * b	Multiply
    * a div b	Divide
    * a mod b	Floating point mod, like Java.

- `a or b` : Boolean `or` operation.

- `a and b` : Boolean `and` operation.

- `(expr)` : Parenthesized expressions.

- `fun(arg1, ..., argn)` : Function calls:

| Function | Supported |
| --- | --- |
`boolean()`| ✓ |
`ceiling()`| ✓ |
`choose()`| ✗ |
`concat()`| ✓ |
`contains()`| ✓ |
`count()`| ✓ |
`current()`| ✗ |
`document()`| ✗ |
`element-available()`| ✗ |
`ends-with()`| ✓ |
`false()`| ✓ |
`floor()`| ✓ |
`format-number()`| ✗ |
`function-available()`| ✗ |
`generate-id()`| ✗ |
`id()`| ✗ |
`key()`| ✗ |
`lang()`| ✗ |
`last()`| ✓ |
`local-name()`| ✓ |
`name()`| ✓ |
`namespace-uri()`| ✓ |
`normalize-space()`| ✓ |
`not()`| ✓ |
`number()`| ✓ |
`position()`| ✓ |
`round()`| ✓ |
`starts-with()`| ✓ |
`string()`| ✓ |
`string-length()`| ✓ |
`substring()`| ✓ |
`substring-after()`| ✓ |
`substring-before()`| ✓ |
`sum()`| ✓ |
`system-property()`| ✗ |
`translate()`| ✓ |
`true()`| ✓ |
`unparsed-entity-url()` | ✗ |