### v1.0.0 2020-09-28
## Overview
This implementation is a subset of the intersection between [JSONPath](https://goessner.net/articles/JsonPath) and [YAML Path](https://pypi.org/project/yamlpath), and it focuses on addressing elements inside YAML files (node descriptors). There are no *query*-like capabilities.
Example YAML structure:
```yaml
foo:
- bar: &bar True
first: First Bar
second: 2
arr: [1, 2, 3]
- baz: False
other_bar: *bar
first: First Baz
some.el/here: Delimiters...
"bar's": 0
```
Example JSON structure:
```json
{
"foo": [
{
"bar": true,
"first": "First Bar",
"second": 2,
"arr": [1, 2, 3]
},
{
"baz": false,
"other_bar": true,
"first": "First Baz",
"some.el/here": "Delimiters...",
"bar's": 0,
}
]
}
```
## Delimiters
Dot-notation (`.`) is the only supported notation to define *map key* path segments. Both *map key* and *sequence index* path segments could also be defined using square brackets (`[`, `]`). For *map key* and *map keys selection* segments both single (`'`) and double (`"`) quotes are supported, `['key']` is the same as `["key"]` and `['key',"other's key"]` is a valid path segment.
For example: `$.foo[0].bar` or `.foo[0]['bar']` or `['foo'][0].bar` or `foo[1]["bar's"]`.
## Special symbols
A path might be prefixed by a dollar sign and a dot (`$`, `.`), but this prefix is retained for compatibility with *JSONPath* and not mandatory. Implicit *document root* is assumed unless the path explicitly starts with an *anchor* (`&...`) segment (see below for details).
If the first segment is a *map key* segment (and explicit *document root* is omitted) the initial dot (`.`) is also not mandatory.
For example, these paths are equal: `$.el`, `.el`, `el`, `['el']`. And they all address the value stored in the "el" key of the top-most map of the document.
An asterisk (`*`) as a key name has a special meaning, and treated as an all-inclusive *keys selection* section (see below). That's it, `$.*` expression would include all keys of the map in the document root. The `[*]` syntax is also valid. One should use the `[:]` notation to acheive same effect for sequences (include all indices).
## Path Segment Types
#### Document Root
`$`
Optional explicit document root. Only allowed to appear at the beginning of the path.
```python
$.foo[0].bar = .foo[0].bar = foo[0].bar
== true
```
#### Map Key
`.map.key` or `.map['key']`
```python
$.foo[0].second = ['foo'][0]['second']
== 2
```
#### Map Keys Selection
`.map['key1','key2',...'keyN']`
Special syntax for the all-inclusive key selection: `.*`. Also, there is the `[*]` variant of this syntax.
```python
$.foo[0]['first','second'] = ['foo'][0]['first','second']
== {"first": "First Bar", "second": 2}
foo[0]['first','second','bar','arr'] = foo[0].*
== {"bar": true, "first": "First Bar", "second": 2, "arr": [1, 2, 3]}
```
#### Sequence Index
`.array[<zero or positive number>]`
```python
$.foo[0]
== {"bar": True, "first": "First Bar", "second": 2}
```
#### Sequence Indices Set
`.array[<zero or positive number>,<zero or positive number>,...<zero or positive number>]`
Special syntax for the all-inclusive indices set: `[:]`.
```python
$.foo[0].arr[0,1,2] = foo[0].arr[:]
== [1, 2, 3]
```
#### Anchor
`&anchor`
Matches elements starting from the given anchor instead of the document root. This segment is only sensible in paths for YAML documents as there is no anchors/aliases concept in the JSON specification.
```python
$.foo[0].bar = &bar
== True
```