# Language introduction¶

This is a overview of the syntax of a NestedText document, which consists of a nested collection of dictionaries, lists, and strings where indentation is used to indicate nesting. All leaf values must be simple text or empty. You can find more specifics in the next section.

## Dictionaries¶

A dictionary is an ordered collection of key value pairs:

key 1: value 1
key 2: value 2
key 3: value 3


A dictionary item is a single key value pair. A dictionary is all adjacent dictionary items in which the keys all begin at the same level of indentation. There are several different ways to specify dictionaries.

In the first form, the key and value are separated by a dictionary tag, which is a colon followed by a space or newline (:␣ or :↵). The key must be a string and must not start with a -␣, >␣, :␣, [, {, #, or white space character; or contain newline characters or the :␣ character sequence. Any spaces between the key and the tag are ignored.

The value of this dictionary item may be a rest-of-line string, a multiline string, a list, or a dictionary. If it is a rest-of-line string, it contains all characters following the tag that separates the key from the value (:␣). For all other values, the rest of the line must be empty, with the value given on the next line, which must be further indented.

key 1: value 1
key 2:
key 3:
- value 3a
- value 3b
key 4:
key 4a: value 4a
key 4b: value 4b
key 5:
> first line of value 5
> second line of value 5


Which is equivalent to the following JSON code:

{
"key 1": "value 1",
"key 2": "",
"key 3": [
"value 3a",
"value 3b"
],
"key 4": {
"key 4a": "value 4a",
"key 4b": "value 4b"
},
"key 5": "first line of value 5\nsecond line of value 5"
}


A second less common form of a dictionary item employs multiline keys. In this case there are no limitations on the key other than it being a string. Each line of a multiline key is introduced with a colon (:) followed by a space or newline. The key is all adjacent lines at the same level that start with a colon tag with the tags removed but leading and trailing white space retained, including all newlines except the last.

This form of dictionary does not allow rest-of-line string values; you would use a multiline string value instead:

: key 1
:     the first key
> value 1
: key 2: the second key
- value 2a
- value 2b


A dictionary may consist of dictionary items of either form.

The final form of a dictionary is the inline dictionary. This is a compact form where all the dictionary items are given on the same line. There is a bit of syntax that defines inline dictionaries, so the keys and values are constrained to avoid ambiguities in the syntax. An inline dictionary starts with an opening brace ({), ends with a matching closing brace (}), and contains inline dictionary items separated by commas (,). An inline dictionary item is a key and value separated by a colon (:). A space need not follow the colon. The keys are inline strings and the values may be inline strings, inline lists, and inline dictionaries. An empty dictionary is represented with {} (there can be no space between the opening and closing braces). Leading and trailing spaces are stripped from keys and string values within inline dictionaries.

For example:

{key 1: value 1, key 2: value 2, key 3: value 3}

{key 1: value 1, key 2: [value 2a, value 2b], key 3: {key 3a: value 3a, key 3b: value 3b}}


## Lists¶

A list is an ordered collection of values:

- value 1
- value 2
- value 3


A list item is introduced with a list tag: a dash followed by a space or a newline at the start of a line (-␣ or -↵). All adjacent list items at the same level of indentation form the list.

The value of a list item may be a rest-of-line string, a multiline string, a list, or a dictionary. If it is a rest-of-line string, it contains all characters that follow the tag that introduces the list item. For all other values, the rest of the line must be empty, with the value given on the next line, which must be further indented.

- value 1
-
-
- value 3a
- value 3b
-
key 4a: value 4a
key 4b: value 4b
-
> first line of value 5
> second line of value 5


Which is equivalent to the following JSON code:

[
"value 1",
"",
[
"value 3a",
"value 3b"
],
{
"key 4a": "value 4a",
"key 4b": "value 4b"
},
"first line of value 5\nsecond line of value 5"
]


Another form of a list is the inline list. This is a compact form where all the list items are given on the same line. There is a bit of syntax that defines the list, so the values are constrained to avoid ambiguities in the syntax. An inline list starts with an opening bracket ([), ends with a matching closing bracket (]), and contains inline values separated by commas. The values may be inline strings, inline lists, and inline dictionaries. An empty list is represented by [] (there should be no space between the opening and closing brackets). Leading and trailing spaces are stripped from string values within inline lists.

For example:

[value 1, value 2, value 3]

[value 1, [value 2a, value 2b], {key 3a: value 3a, key 3b: value 3b}]


[ ] is not treated as an empty list as there is space between the brackets, rather this represents a list with a single empty string value. The contents of the brackets, which consists only of white space, is stripped of its padding, leaving an empty string.

## Strings¶

There are three types of strings: rest-of-line strings, multiline strings, and inline strings. Rest-of-line strings are simply all the characters on a line that follow a list tag (-␣) or dictionary tag (:␣), including any leading or trailing white space. They can contain any character other than a newline. The content of the rest-of-line string starts after the first space that follows the dash or colon of the tag:

code   : input signed [7:0] level
regex  : [+-]?([0-9]*[.])?[0-9]+\s*\w*
math   : $x = \frac{{-b \pm \sqrt {b^2 - 4ac}}}{2a}$
unicode: José and François


Multi-line strings are all adjacent lines that are prefixed with a string tag; the greater-than symbol followed by a space or a newline (>␣ or >↵). The content of each line starts after the first space that follows the greater-than symbol:

>     This is the first line of a multiline string, it is indented.
> This is the second line, it is not indented.


You can include empty lines in the string simply by specifying the greater-than symbol alone on a line:

>
> “The worth of a man to his society can be measured by the contribution he
>  makes to it — less the cost of sustaining himself and his mistakes in it.”
>
>                                                — Erik Jonsson
>


The multiline string is all adjacent lines that start with a string tag with the tags removed and the lines joined together with newline characters inserted between each line. Except for the space that follows the > in the tag, white space from both the beginning and the end of each line is retained, along with all newlines except the last.

Inline strings are the string values specified in inline dictionaries and lists. They are somewhat constrained in the characters that they may contain; nothing that might be confused with the syntax characters used by the inline list or dictionary that contains it. Specifically, inline strings may not contain newlines or any of the following characters: [, ], {, }, or ,. In addition, inline strings that are contained in inline dictionaries may not contain :. Leading and trailing white space are ignored with inline strings.

Lines that begin with a hash as the first non-white-space character, or lines that are empty or consist only of white space are comment lines and are ignored. Indentation is not significant on comment lines.

# this line is ignored

# this line is also ignored, as is the blank line above.


Comment lines are ignored when determining whether adjacent lines belong to the same dictionary, list, or string. For example, the following represents one multiline string:

> this is the first line of a multiline string
# this line is ignored
> this is the second line of the multiline string


## Nesting¶

A value for a dictionary or list item may be a rest-of-line string or it may be a nested dictionary, list, multiline string, or inline dictionary or list. Indentation is used to indicate nesting. Indentation increases to indicate the beginning of a new nested object, and indentation returns to a prior level to indicate its end. In this way, data can be nested to an arbitrary depth:

# Contact information for our officers

Katheryn McDaniel:
position: president
> 138 Almond Street
> Topeka, Kansas 20697
phone:
cell: 1-210-555-5297
work: 1-210-555-3423
home: 1-210-555-8470
# Katheryn prefers that we always call her on her cell phone.
email: KateMcD@aol.com
kids:
- Joanie
- Terrance

Margaret Hodge:
position: vice president
> 2586 Marigold Lane
> Topeka, Kansas 20697
phone:
{cell: 1-470-555-0398, home: 1-470-555-7570}
email: margaret.hodge@ku.edu
kids:
[Arnie, Zach, Maggie]


It is recommended that each level of indentation be represented by a consistent number of spaces (with the suggested number being 2 or 4). However, it is not required. Any increase in the number of spaces in the indentation represents an indent and the number of spaces need only be consistent over the length of the nested object.

The data can be nested arbitrarily deeply.

## NestedText Files¶

NestedText files should be encoded with UTF-8 and should end with a newline. The top-level object must not be indented.

The name used for the file is arbitrary but it is tradition to use a .nt suffix. If you also wish to further distinguish the file type by giving the schema, it is recommended that you use two suffixes, with the suffix that specifies the schema given first and .nt given last. For example: officers.addr.nt.