add notes for base64url Encodings (#416)

* add notes to clarify the behavior for base64url encoded values.

* improve first note on encoding

Author: sebbader-sap

documentation/IDTA-01002-3/modules/ROOT/pages/changelog.adoc

@@ -40,6 +40,7 @@ Minor Changes:
 
 * Clarification on how to handle duplicate query parameters
 * Replace "servers" clause in OpenAPI files
+* Add notes for base64url-encoded values and order of "assetIds" query parameters
 
 === Interface Changes w.r.t. V3.0.3 to V3.1
 

documentation/IDTA-01002-3/modules/ROOT/pages/http-rest-api/http-rest-api.adoc

@@ -85,11 +85,21 @@ A list of base64url-encoded ids is simply passed as comma-separated query parame
 * Please note that base64url-encoding differs slightly from base64-encoding and has been specifically defined for passing URLs.
 An appropriate base64url implementation needs to be used for encoding/decoding.
 See RFC 4648 for further details.
+
+====
+Note: Encoding JSON objects may lead to different encoded strings, depending e.g. whether control characters (white spaces, line-breaks etc.) are included or not. However, servers must be able to deal with included control characters and operate on the original content.
+====
+
 * When base64url or base64-encoding is mentioned in connection with string values (e.g. Identifiers), the UTF-8 decoded byte array representation of that string is used for the base64url or base64-encoding.
 * When retrieving AssetAdministrationShells (/shells, /lookup/shells), a query parameter “?assetids=” can be specified.
 Such assetId may be a globalAssetId or specificAssetId.
 The corresponding key-value-pair is first serialized to JSON and then base64url-encoded.
 The resulting encoded string is the value of “?assetids=”.
+
+====
+Note: In case more than one globalAssetId or specificAssetId is provided, their order shall not affect the result.
+====
+
 * In some operations, references are part of the query parameters e.g. “?semanticId=”.
 The corresponding reference is first serialized to JSON and then base64url-encoded.
 The resulting encoded string is the value of “?semanticId=”.
@@ -178,7 +188,7 @@ Technically, the idShortPath is a string and the idShorts are separated by a dot
 
 .Example Hierarchy of Submodel Elements
 [[se-hierarchy]]
-image::se-hierarchy.jpeg[image24,width=642,height=367]
+image::se-hierarchy.png[image24,width=642,height=367]
 
 The example hierarchy in <<se-hierarchy>> shows a Submodel with a hierarchical structure of SubmodelElements.
 The submodel can be addressed by its global identifier “https://admin-shell.io/sampleSM”.