fixed docs for issue #2968 (#2980)

CHANGELOG

@@ -1,6 +1,8 @@
 devel
 -----
 
+* fixed docs for issue #2968
+
 * AQL CHAR_LENGTH(null) returns now 0. Since AQL TO_STRING(null) is '' (string of length 0)
 
 * ui: now supports single js file upload for foxx services in addition to zip files

Documentation/Books/HTTP/Collection/README.md

@@ -62,9 +62,15 @@ When creating a collection with the auto increment key generator and an incremen
 
 1, 6, 11, 16, 21, ...
 
+The auto-increment values are increased and handed out on each document insert 
+attempt. Even if an insert fails, the auto-increment value is never rolled back.
+That means there may exist gaps in the sequence of assigned auto-increment values
+if inserts fails.
+
 The basic operations (create, read, update, delete) for documents are mapped
 to the standard HTTP methods (*POST*, *GET*, *PUT*, *DELETE*). 
 
+
 Address of a Collection
 -----------------------
 

Documentation/Books/Manual/DataModeling/Collections/DatabaseMethods.md

@@ -87,7 +87,7 @@ to the [naming conventions](../NamingConventions/README.md).
   This option is meaningful for the MMFiles storage engine only.
 
 - *keyOptions* (optional): additional options for key generation. If
-  specified, then *keyOptions* should be a JSON array containing the
+  specified, then *keyOptions* should be a JSON object containing the
   following attributes (**note**: some of them are optional):
   - *type*: specifies the type of the key generator. The currently
     available generators are *traditional* and *autoincrement*.