Keys

A key identifies a configuration entry. In an entry, the key is followed by whitespace and then a value. In a prefix block, the key is followed by whitespace and then {.

There are two kinds of keys: word keys and quoted keys.

The separator between a key and a value must be spaces. Tab characters in the separator position are not allowed and produce a parse error (see Key-Value Separator).

Word Key

A word key is a contiguous sequence of non-whitespace characters. It is terminated by the first space, tab, newline, or EOF.

The set of characters that can start a word key is broad: letters, digits, punctuation marks such as ., -, +, |, >, {, }, and essentially any character that is not whitespace or a quote. Notably, tokens like true, false, and numeric literals (42, -5) are valid word keys when they appear in key position.

hello     world
42        value
-57       value
+13       value
true      value
false     value
server.port 8080

In all cases above, the first token on the line is the key and the text after the separating space is the value. Because 42, -57, true, etc. are followed by content, they are parsed as word keys, not as typed values.

A word key consumes all characters until whitespace or EOF, regardless of what those characters are. This means braces embedded within other characters are part of the key:

foo{    value
a{b     value

These produce the keys foo{ and a{b.

Word key errors

A key alone on a line with no value is a parse error:

lonely

This produces the error: “missing value for the key”.

Quoted Key

A quoted key is enclosed in matching double quotes ("...") or single quotes ('...'). Quoted keys may contain any character that is valid in a string literal, including spaces. Empty quoted keys are allowed.

"double"            value
'single'            value
"key with spaces"   value
""                  value
''                  value

Escape sequences inside quoted keys follow the same rules as quoted strings: \\ and the matching quote character can be escaped with a backslash.

Quoted key errors

After the closing quote, the next character must be whitespace (space, tab, newline) or EOF. If non-whitespace characters appear immediately after the closing quote, a parse error is produced:

"quoted"ppp value

This produces the error: “unexpected token after quoted key”. The characters after the closing quote are discarded, and if a valid value follows a space, it is still parsed.

An unclosed quoted key (where the closing quote is missing before the end of the line) produces the error: “missing closing quote”. Since the entire line is consumed into the key, no value is present and an additional error “missing value for the key” is produced.

"unterminated value

Key-Value Separator

The key and the value are separated by one or more spaces. Multiple spaces between the key and the value are allowed and are purely cosmetic:

a  value
b   42
c    true

Tab characters between the key and the value produce the error: “tab separating is not allowed”.

Duplicate Keys

Multiple entries may share the same key. Each occurrence is a distinct entry and all are preserved in the evaluated output.

tag  web
tag  server
tag  production

{
  "tag": ["web", "server", "production"]
}

This produces three entries, all with the key tag. No entry is overwritten or merged.

The same rule applies to keys formed by prefix concatenation:

item. {
  tag important
}
item. {
  tag urgent
}

{
  "item.tag": ["important", "urgent"]
}

Both entries with key item.tag are preserved.