Lack of lexical token delimiter specification

It seems that the current JMESPath specification doesn't specify any lexical token delimiters, which leaves ambiguity and confusion.

For example, considering the following two grammar rules in the spec:

```
comparator-expression = expression comparator expression
raw-string = "'" *raw-string-char "'"
```

Sub-rules are concatenated in the same way in the above two rules but clearly the first one allows white spaces between `expression` and `comparator` since we have the following official example in the examples page:

```
people[?age > `20`].[name, age]
```

while white spaces are not allowed between `"'"` and `*raw-string-char` since a `raw-string` is expected to be a single lexical token.

After studying RFC 4234, I foud the following statements in [section 3.1][1]:

```
LINEAR WHITE SPACE: Concatenation is at the core of the ABNF parsing
model. A string of contiguous characters (values) is parsed
according to the rules defined in ABNF. For Internet specifications,
there is some history of permitting linear white space (space and
horizontal tab) to be freely and implicitly interspersed around major
constructs, such as delimiting special characters or atomic strings.

NOTE:

This specification for ABNF does not provide for implicit
specification of linear white space.

Any grammar that wishes to permit linear white space around
delimiters or string segments must specify it explicitly. It is
often useful to provide for such white space in "core" rules that are
then used variously among higher-level rules. The "core" rules might
be formed into a lexical analyzer or simply be part of the main
ruleset.
```

Shall we specify lexical token delimiters explicitly and distinguish lexical rules from grammar rules to eliminate the ambiguity?

[1]: https://tools.ietf.org/html/rfc4234#section-3.1