Add support for XEP-0394: Message Markup

Fixes SMACK-794.

documentation/extensions/index.md

@@ -98,6 +98,7 @@ Experimental Smack Extensions and currently supported XEPs of smack-experimental
 | [OMEMO Multi End Message and Object Encryption](omemo.md)            | [XEP-XXXX](https://conversations.im/omemo/xep-omemo.html) | Encrypt messages using OMEMO encryption (currently only with smack-omemo-signal -> GPLv3). |
 | [Consistent Color Generation](consistent_colors.md) | [XEP-0392](http://xmpp.org/extensions/xep-0392.html) | Generate consistent colors for identifiers like usernames to provide a consistent user experience. |
 | Google GCM JSON payload                     | n/a                                                  | Semantically the same as XEP-0335: JSON Containers |
+| [Message Markup](messagemarkup.md)          | [XEP-0394](http://xmpp.org/extensions/xep-0394.html)| Style message bodies while keeping body and markup information separated. |
 
 
 Legacy Smack Extensions and currently supported XEPs of smack-legacy

documentation/extensions/messagemarkup.md

@@ -0,0 +1,68 @@
+Message Markup
+==============
+
+[Back](index.md)
+
+[Message Markup (XEP-0394)](https://xmpp.org/extensions/xep-0394.html) can be used as a an alternative to XHTML-IM to style messages, while keeping the body and markup information strictly separated.
+This implementation can *not* be used to render message bodies, but will offer a simple to use interface for creating ExtensionElements which encode the markup information.
+
+## Usage
+
+The most important class is the `MarkupElement` class, which contains a Builder.
+
+To start creating a Message Markup Extension, call `MarkupElement.getBuilder()`.
+(Almost) all method calls documented below will be made on the builder.
+
+Whenever a method call receives a `start` and `end` index, `start` represents the first character, which is affected by the styling, while `end` is the character *after* the last affected character.
+
+### Inline styling
+
+Currently there are 3 styles available:
+* *emphasis*, which should be rendered by a client as *italic*, or **bold**
+* *code*, which should be rendered in `monospace`
+* *deleted*, which should be rendered as ~~strikethrough~~.
+
+Those styles are available by calling `builder.setEmphasis(int start, int end)`,
+`builder.setDeleted(int start, int end)` and `builder.setCode(int start, int end)`.
+
+If you want to apply multiple inline styles to a section, you can do the following:
+```
+Set<SpanElement.SpanStyle> spanStyles = new HashSet<>();
+styles.add(SpanElement.SpanStyle.emphasis);
+styles.add(SpanElement.SpanStyle.deleted);
+builder.addSpan(start, end, spanStyles);
+```
+
+Note, that spans cannot overlap one another.
+
+### Block Level Styling
+
+Available block level styles are:
+* Code blocks, which should be rendered as
+```
+blocks
+of
+code
+```
+
+* Itemized lists, which should render as
+  * Lists
+  * with possibly multiple
+  * entries
+
+* Block Quotes, which should be rendered by the client
+  > as quotes, which
+  >> also can be nested
+
+To mark a section as code block, call `builder.setCodeBlock(start, end)`.
+
+To create a list, call `MarkupElement.Builder.ListBuilder lbuilder = builder.beginList()`, which will return a list builder.
+On this you can call `lbuilder.addEntry(start, end)` to add an entry.
+
+Note: If you add an entry, the start value MUST be equal to the end value of the previous added entry!
+
+To end the list, call `lbuilder.endList()`, which will return the MessageMarkup builder.
+
+To create a block quote, call `builder.setBlockQuote(start, end)`.
+
+Note that block level elements MUST NOT overlap each other boundaries, but may be fully contained (nested) within each other.