Update to show the javadoc global attribute.

src/docs/asciidoc/wiki/wiki_header.adoc

@@ -18,6 +18,7 @@ All wiki documents use these header attributes. Optional attributes can be left
 :relfileprefix: ../../
 :imagesdir: ../..
 :experimental:
+:link-javadoc: https://javadoc.jmonkeyengine.org
 ifdef++::++env-github,env-browser[:outfilesuffix: .adoc]
 ----
 
@@ -29,21 +30,25 @@ ifdef++::++env-github,env-browser[:outfilesuffix: .adoc]
 
 *pass:[:]revdate:* Optional. Revision Date
 
-*pass:[:]relfileprefix:* Mandatory. Enter a path to the "`asciidoc`" folder.
+*pass:[:]relfileprefix:* Optional. Enter a path to the "`asciidoc`" folder if using cross reference links.
 
 TIP: Use `Tree View` (kbd:[ctrl]+kbd:[\ ] or `menu:View[Toggle Tree View]`) to locate the "`asciidoc`" folder if using the link:https://atom.io/[Atom editor].
 
 In the example below, "`asciidoc`" is two folders above the folder this file is located in.
 
-`pass:[:]relfileprefix: ../../`
+```
+:relfileprefix: ../../
+```
 
-*pass:[:]imagesdir:* Mandatory. Enter a path to the "images" folder.
+*pass:[:]imagesdir:* Optional. Enter a path to the "images" folder if using image links.
 
 TIP: Use `Tree View` (kbd:[ctrl]+kbd:[\ ] or `menu:View[Toggle Tree View]`) to locate the "`images`" folder if using the link:https://atom.io/[Atom editor].
 
 In the example below, "`images`" is two folders above the folder this file is located in. Note the missing kbd:[/] forward slash.
 
-`pass:[:]imagesdir: ../..`
+```
+:imagesdir: ../..
+```
 
 [TIP]
 ====
@@ -62,4 +67,12 @@ The "`images`" folder resides in the same folder as the "`asciidoc`" folder so i
 
 *pass:[:]experimental:* Leave this blank. This is the experimental attribute that allows the use of link:http://asciidoctor.org/docs/user-manual/#user-interface-macros[User Interface Macros]. You use these macros for creating keyboard shortcuts, displaying menu selections and UI buttons.
 
+*pass:[:]link-javadoc:* Optional. This is the global attribute for the jME javadocs. You set this if you are *overriding* the default setting from the link:https://github.com/jMonkeyEngine/wiki/blob/9d0e4fd07d019c3d41c6b9e64b2a1a5b7e0ed774/build.gradle#L39[build.gradle] file. You can use the default `{link-javadoc}` attribute directly in any document you write, as is shown in the following example, without adding anything to the header.
+
+```
+link:{link-javadoc}/com/jme3/app/state/BaseAppState.html[BaseAppState]
+```
+
+If you override the variable in the header of the document, that value will be used instead.
+
 *ifdef++::++env-github,env-browser[:outfilesuffix: .adoc]* See link:http://asciidoctor.org/docs/user-manual/#navigating-between-source-files[Navigating Between Source Files] in the AsciiDoctor user manual. Leave this as written.