FIXED - method calls inside dot chain.

doc/src/engine/custom-syntax.md

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+Custom Syntax
+=============
+
+{{#include ../links.md}}
+

doc/src/engine/dsl.md

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+Use Rhai as a Domain-Specific Language (DSL)
+===========================================
+
+{{#include ../links.md}}
+
+Rhai can be successfully used as a domain-specific language (DSL).
+
+
+Expressions Only
+----------------
+
+In many DSL scenarios, only evaluation of expressions is needed.
+
+The `Engine::eval_expression_XXX`[`eval_expression`] API can be used to restrict
+a script to expressions only.
+
+
+Disable Keywords and/or Operators
+--------------------------------
+
+In some DSL scenarios, it is necessary to further restrict the language to exclude certain
+language features that are not necessary or dangerous to the application.
+
+For example, a DSL may disable the `while` loop altogether while keeping all other statement
+types intact.
+
+It is possible, in Rhai, to surgically [disable keywords and operators].
+
+
+Custom Operators
+----------------
+
+On the other hand, some DSL scenarios require special operators that make sense only for
+that specific environment.  In such cases, it is possible to define [custom operators] in Rhai.
+
+For example:
+
+```rust
+let animal = "rabbit";
+let food = "carrot";
+
+animal eats food            // custom operator - 'eats'
+
+eats(animal, food)          // <- the above really de-sugars to this
+```
+
+Although a [custom operator] always de-sugars to a simple function call,
+nevertheless it makes the DSL syntax much simpler and expressive.
+
+
+Custom Syntax
+-------------
+
+For advanced DSL scenarios, it is possible to define entire expression [_syntax_][custom syntax] -
+essentially custom statement types.
+
+The [`internals`] feature is needed to be able to define [custom syntax] in Rhai.
+
+For example:
+
+```rust
+let table = [..., ..., ..., ...];
+
+// Syntax = "select" $ident$ $ident$ "from" $expr$ "->" $ident$ ":" $expr$
+let total = select sum price from table -> row : row.weight > 50;
+```
+
+After registering this custom syntax with Rhai, it can be used anywhere inside a script as
+a normal expression.
+
+For its evaluation, the callback function will receive the following list of parameters:
+
+`exprs[0] = "sum"` - math operator  
+`exprs[1] = "price"` - field name  
+`exprs[2] = Expr(table)` - data source  
+`exprs[3] = "row"` - loop variable name  
+`exprs[4] = Expr(row.wright > 50)` - expression  
+
+The other identified, such as `"select"`, `"from"`, as as as symbols `->` and `:` are
+parsed in the order defined within the custom syntax.