Enhance description of bind parameters

Documentation/Books/AQL/Fundamentals/BindParameters.mdpp

@@ -10,9 +10,10 @@ query.
 Using bind parameters, the meaning of an existing query cannot be changed. Bind
 parameters can be used everywhere in a query where literals can be used.
 
-The syntax for bind parameters is *@name* where *name* is the
-actual parameter name. The bind parameter values need to be passed along with
-the query when it is executed, but not as part of the query text itself.
+The syntax for bind parameters is *@name* where *@* signifies that this is a
+bind parameter and *name* is the actual parameter name. Parameter names must
+start with any of the letters *a* to *z* (upper or lower case) or a digit
+(*0* to *9*), and can be followed by any letter, digit or the underscore symbol.
 
 ```js
 FOR u IN users
@@ -20,13 +21,38 @@ FOR u IN users
   RETURN u
 ```
 
-Bind parameter names must start with any of the letters *a* to *z* (both in
-lower and upper case) or a digit (*0* to *9*), and can be followed by any
-letter, digit or the underscore symbol.
+The bind parameter values need to be passed along with the query when it is
+executed, but not as part of the query text itself. In the web interface,
+there is a pane next to the query editor where the bind parameters can be
+entered. When using `db._query()` (in arangosh for instance), then an
+object of key-value pairs can be passed for the parameters. Such an object
+can also be passed to the HTTP API endpoint `_api/cursor`, as attribute
+value for the key *bindVars*:
 
-Bind variables represent a value like a string, and must not be put in quotes.
-If you need to do string processing (concatenation, etc.) in the AQL query, you need
-to use [string functions](../Functions/String.md) to do so:
+```json
+{
+  "query": "FOR u IN users FILTER u.id == @id && u.name == @name RETURN u",
+  "bindVars": {
+    "id": 123,
+    "name": "John Smith"
+  }
+}
+```
+
+Bind parameters that are declared in the query must also be passed a parameter
+value, or the query will fail. Specifying parameters that are not declared in
+the query will result in an error too.
+
+Bind variables represent a value like a string, and must not be put in quotes
+in the AQL code:
+
+```js
+FILTER u.name == "@name" // wrong
+FILTER u.name == @name   // correct
+```
+
+If you need to do string processing (concatenation, etc.) in the query, you
+need to use [string functions](../Functions/String.md) to do so:
 
 ```js
 FOR u IN users
@@ -34,6 +60,44 @@ FOR u IN users
   RETURN u
 ```
 
+Bind paramers can be used for both, the dot notation as well as the square
+bracket notation for sub-attribute access. They can also be chained:
+
+```js
+LET doc = { foo: { bar: "baz" } }
+
+RETURN doc.@attr.@subattr
+// or
+RETURN doc[@attr][@subattr]
+```
+
+```json
+{
+  "attr": "foo",
+  "subattr": "bar"
+}
+```
+
+Both variants in above example return `[ "baz" ]` as query result.
+
+The whole attribute path, for highly nested data in particular, can also be
+specified using the dot notation and a single bind parameter, by passing an
+array of strings as parameter value. The elements of the array represent the
+attribute keys of the path:
+
+```js
+LET doc = { a: { b: { c: 1 } } }
+RETURN doc.@attr
+```
+
+```json
+{ "attr": [ "a", "b", "c" ] }
+```
+
+The example query returns `[ 1 ]` as result. Note that `{ "attr": "a.b.c" }`
+would return the value of an attribute called *a.b.c*, not the value of
+attribute *c* with the parents *a* and *b* as `[ "a", "b", "c" ]` would.
+
 A special type of bind parameter exists for injecting collection names. This
 type of bind parameter has a name prefixed with an additional *@* symbol (thus
 when using the bind parameter in a query, two *@* symbols must be used).
@@ -44,8 +108,12 @@ FOR u IN @@collection
   RETURN u
 ```
 
+```json
+{ "@collection": "myCollection" }
+```
+
 Specific information about parameters binding can also be found in:
 
 - [AQL with Web Interface](../Invocation/WithWebInterface.md)
 - [AQL with Arangosh](../Invocation/WithArangosh.md)
-- [HTTP Interface for AQL Queries](../../HTTP/AqlQuery/index.html)
+- [HTTP Interface for AQL Queries](../../HTTP/AqlQueryCursor/index.html)