diff --git a/Changes b/Changes
index ede43f5..646b434 100644
--- a/Changes
+++ b/Changes
@@ -18,7 +18,8 @@
 	  renamed KorapResponse to Response,
 	  moved model/* to index,
 	  moved meta/SearchContext to response/SearchContext,
-	  krillified property files (diewald)
+	  krillified property files,
+	  added Errorcodes (diewald)
         - [documentation] Improved documentation for API classes (diewald)
 
 0.50 2015-02-23
diff --git a/Errorcodes b/Errorcodes
new file mode 100644
index 0000000..537da15
--- /dev/null
+++ b/Errorcodes
@@ -0,0 +1,78 @@
+* 600 - 699 - Lucene Backend error codes
+600: "Unable to read index"
+601: "Unable to find index"
+602: "Unable to add document to index"
+603: "Unable to commit staged data to index"
+604: "Unable to connect to database"
+610: "Missing request parameters"
+620: "Unable to generate JSON"
+621: "Unable to parse JSON"
+680: "Server is up and running!"
+681: "Document was added successfully", document id
+682: "Response time exceeded"
+
+* 700 - 799 - Coral Deserialization errors
+700: "No Query given"
+701: "JSON-LD group has no @type attribute"
+702: "Boundary definition is invalid"
+703: "Group expects operation"
+704: "Operation needs operand list"
+705: "Number of operands is not acceptable"
+706: "Frame type is unknown"
+707: "Distance Constraints have to be defined as arrays"
+708: "No valid distances defined"
+709: "Valid class numbers exceeded"
+710: "Class attribute missing"
+711: "Unknown group operation"
+712: "Unknown reference operation"
+713: "Query type is not supported"
+714: "Span references expect a start position and a length parameter"
+715: "Attribute type is not supported"
+716: "Unknown relation"
+740: "Key definition is missing in term or span"
+741: "Match relation unknown"
+742: "Term group needs operand list"
+743: "Term group expects a relation"
+744: "Operand not supported in term group"
+745: "Token type is not supported"
+746: "Term type is not supported - treated as a string"
+747: "Attribute is null"
+750: "Passed notifications are not well formed"
+760: "Exclusion is currently not supported in position operations"
+761: "Class reference operators are currently not supported"
+762: "Span references are currently not supported" (Not in use)
+763: "Excluding distance constraints are currently not supported"
+764: "Class reference checks are currently not supported - results may not be correct"
+765: "Relations are currently not supported"
+766: "Peripheral references are currently not supported"
+767: "Case insensitivity is currently not supported for this layer"
+768: "Attributes are currently not supported - results may not be correct"
+769: "Overlap variant currently interpreted as overlap"
+770: "Arity attributes are currently not supported - results may not be correct"
+771: "Arbitrary elements with attributes are currently not supported"
+780: "This query matches everywhere"
+781: "Optionality of query is ignored"
+782: "Exclusivity of query is ignored"
+799: Unknown query serialization message (Arbitrary string)
+
+* 800 - 899 - Virtual Collection Messages
+802: "Match type is not supported by value type"
+804: "Unknown value type"
+805: "Value is invalid"
+806: "Value is not a valid date string"
+807: "Value is not a valid regular expression"
+810: "Unknown document group operation" (like 711)
+811: "Document group expects operation" (like 703)
+812: "Operand not supported in document group" (like 744)
+813: "Collection type is not supported" (like 713)
+814: "Unknown rewrite operation"
+815: "Rewrite expects source"
+830: "Filter was empty"
+831: "Filter is not wrappable"
+832: "Filter operation is invalid"
+850: "Collections are deprecated in favour of a single collection"
+851: "Legacy filters need @value fields"
+
+* 900 - 999 - Corpus Data errors
+952: "Given offset information is not numeric"
+953: "Given offset information is incomplete"
\ No newline at end of file
diff --git a/src/main/java/de/ids_mannheim/korap/Krill.java b/src/main/java/de/ids_mannheim/korap/Krill.java
index 6fb9fb1..0fdf5d0 100644
--- a/src/main/java/de/ids_mannheim/korap/Krill.java
+++ b/src/main/java/de/ids_mannheim/korap/Krill.java
@@ -18,17 +18,30 @@
 import org.slf4j.LoggerFactory;
 
 /**
- * Krill is a corpus data retrieval index using Lucene for Look-Ups.
+ * <p>Krill is a corpus data retrieval index using Lucene for Look-Ups.</p>
+ *
+ * <p>
  * It is the reference implementation for KoralQuery consumption,
- * and supports specified query and collection objects,
- * and proprietary meta objects.
+ * and this class acts as the central point for consuming and
+ * responding to KoralQuery requests.
+ * </p>
+ *
+ * <p>
+ * The processing of the collection section of the request is delegated
+ * to {@link KrillCollection}, the query section to {@link KrillQuery},
+ * and the meta section to {@link KrillMeta}.
+ * </p>
  *
  * <blockquote><pre>
- *   // Create a new krill search object by passing a KoralQuery string
- *   Krill krill = new Krill(koralQueryString);
+ *   // Create or receive a KoralQuery JSON string
+ *   String koral = "{\"query\":{...}, \"collection\":{...}, ... }";
+ *
+ *   // Create a new krill search object by passing the Query
+ *   Krill krill = new Krill(koral);
  *
  *   // Apply the query to an index and receive a search result
- *   Result result = krill.apply(new KrillIndex());
+ *   // This may invoke different actions depending on the request
+ *   Result result = krill.setIndex(new KrillIndex()).apply();
  * </pre></blockquote>
  *
  * @author diewald
@@ -39,9 +52,7 @@
  * @see KrillMeta
  * @see KrillIndex
  */
-/*
- * Todo: Use a configuration file
- */
+// Todo: Use a krill.properties configuration file
 public class Krill extends Response {
     private KrillIndex index;
     private SpanQuery spanQuery;
@@ -153,6 +164,7 @@
                     this.addError(780, "This query matches everywhere");
 
                 else {
+
                     // Serialize a Lucene SpanQuery based on the SpanQueryWrapper
                     this.spanQuery = qw.toQuery();
 
@@ -182,7 +194,7 @@
         // Copy notifications from request
         this.copyNotificationsFrom(json);
 	    
-        // Parse virtual collections
+        // Parse "collection" or "collections" attribute
         try {
             if (json.has("collection")) {
                 this.setCollection(
@@ -205,7 +217,7 @@
             this.addError(q.getErrorCode(), q.getMessage());
         };
 
-        // Parse meta object
+        // Parse "meta" attribute
         if (!this.hasErrors() && json.has("meta"))
             this.setMeta(new KrillMeta(json.get("meta")));
 
@@ -224,7 +236,7 @@
 
 
     /**
-     * Set the associated {@link KrillIndex} object.
+     * Set the {@link KrillIndex} object.
      *
      * @param index The associated {@link KrillIndex} object.
      * @return The {@link Krill} object for chaining.
@@ -237,6 +249,9 @@
 
     /**
      * Apply the KoralQuery to an index.
+     * This may invoke different actions depending
+     * on the meta information, like {@link KrillIndex#search}
+     * or {@link KrillIndex#collect}.
      *
      * @param index The {@link KrillIndex}
      *        the search should be applyied to.
@@ -249,6 +264,9 @@
 
     /**
      * Apply the KoralQuery to an index.
+     * This may invoke different actions depending
+     * on the meta information, like {@link KrillIndex#search}
+     * or {@link KrillIndex#collect}.
      *
      * @return The result as a {@link Result} object.
      */
diff --git a/src/main/java/de/ids_mannheim/korap/KrillQuery.java b/src/main/java/de/ids_mannheim/korap/KrillQuery.java
index d7b68dc..7ad031e 100644
--- a/src/main/java/de/ids_mannheim/korap/KrillQuery.java
+++ b/src/main/java/de/ids_mannheim/korap/KrillQuery.java
@@ -19,10 +19,15 @@
 import de.ids_mannheim.korap.util.QueryException;
 
 /**
+ * <p>
  * KrillQuery provides deserialization methods
  * for KoralQuery query objects.
+ * </p>
  *
  * <blockquote><pre>
+ *   // Create or receive a KoralQuery JSON string
+ *   String koral = "{\"@type\":"koral:group", ... }";
+ *
  *   SpanQueryWrapper sqw = new KrillQuery("tokens").fromJson("{... JsonString ...}");
  * </pre></blockquote>
  *
@@ -37,7 +42,7 @@
   e.g. der alte []
   should be wrapped in a contains(<base/s=t>) to ensure
   they are not outside the text.
-
+  
   TODO: Create Pre-filter while preparing a Query.
   The pre-filter will contain a boolena query with all
   necessary terms, supporting boolean OR, ignoring
@@ -46,8 +51,8 @@
   Search for all documents containing "s:Der" and ("s:alte" or "s:junge") and "s:Mann"
 */
 public class KrillQuery extends Notifications {
-    private String field;
     private QueryBuilder builder;
+    private String field;
     private JsonNode json;
 
     // Logger
@@ -69,19 +74,6 @@
 
     private static final int MAX_CLASS_NUM = 255; // 127;
 
-    /**
-     * Constructs a new object for query deserialization
-     * and building. Expects the name of an index field
-     * to apply the query on (this should normally be
-     * a token stream field).
-     *
-     * @param field The specific index field for the query.
-     */
-    public KrillQuery (String field) {
-        this.field = field;
-    };
-
-
     // Private class for koral:boundary objects
     private class Boundary {
         public int min, max;
@@ -117,17 +109,33 @@
         };
     };
 
+    /**
+     * Constructs a new object for query deserialization
+     * and building. Expects the name of an index field
+     * to apply the query on (this should normally be
+     * a token stream field).
+     *
+     * @param field The specific index field for the query.
+     */
+    public KrillQuery (String field) {
+        this.field = field;
+    };
+
 
     /**
-     * Deserialize JSON-LD query to a {@link SpanQueryWrapper} object.
+     * <p>Deserialize JSON-LD query to a {@link SpanQueryWrapper} object.</p>
      *
-     * <p>
      * <blockquote><pre>
      *   KrillQuery kq = new KrillQuery("tokens");
-     *   SpanQueryWrapper sqw = kq.fromJson('{"@type":"koral:token","wrap":{' +
-     *      '"@type":"koral:term","foundry":"opennlp",' +
-     *      '"key":"tree","layer":"orth",' +
-     *      '"match":"match:eq"}}'
+     *   SpanQueryWrapper sqw = kq.fromJson(
+     *     "{\"@type\" : \"koral:token\","+
+     *      "\"wrap\" : {" +
+     *        "\"@type\" :   \"koral:term\"," +
+     *        "\"foundry\" : \"opennlp\"," +
+     *        "\"key\" :     \"tree\"," +
+     *        "\"layer\" :   \"orth\"," +
+     *        "\"match\" :   \"match:eq\""+
+     *      "}}"
      *   );
      * </pre></blockquote>
      *
@@ -159,18 +167,22 @@
 
 
     /**
-     * Deserialize JSON-LD query as a {@link JsonNode} object
-     * to a {@link SpanQueryWrapper} object.
+     * <p>Deserialize JSON-LD query as a {@link JsonNode} object
+     * to a {@link SpanQueryWrapper} object.</p>
      *
      * @param json {@link JsonNode} representing the JSON query string.
      * @return {@link SpanQueryWrapper} object. 
      * @throws QueryException
      */
     // TODO: Exception messages are horrible!
-    // TODO: Use the shortcuts implemented in this class instead of the wrapper constructors
+    // TODO: Use the shortcuts implemented in the builder
+    //       instead of the wrapper constructors
     // TODO: Rename this span context!
     public SpanQueryWrapper fromJson (JsonNode json) throws QueryException {
         int number = 0;
+
+        // Only accept @typed objects for the moment
+        // TODO: Support @context for cosmas:...
         if (!json.has("@type"))
             throw new QueryException(701, "JSON-LD group has no @type attribute");
 
@@ -276,8 +288,16 @@
 
 
     /**
+     * <p>
      * Get the associated {@link QueryBuilder} object
      * for query building.
+     * </p>
+     *
+     * <blockquote><pre>
+     *   SpanQueryWrapper query = new KrillQuery("tokens").builder().re("mate/p=N.*");
+     * </pre></blockquote>
+     *
+     * @return The {@link QueryBuilder}.
      */
     public QueryBuilder builder () {
         if (this.builder == null)