Docu: Update core expression document with selection variable and fix markdown

Add org.eclipse.ui.selection variable to the variables table and fix
markdown rendering throughout the document by wrapping XML elements
in backticks so they display correctly. Also update section titles
to use title case for consistency.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: vogella

docs/Command_Core_Expressions.md

@@ -7,14 +7,14 @@ Core expressions are declarative or programmatic expressions based on the org.ec
 Expressions and the Command Framework
 =====================================
 
-The [Platform Command Framework](PlatformCommandFramework.md) uses [core expressions](Platform_Expression_Framework.md) for enabledWhen and activeWhen for handlers, programmatic activation of contexts, and for visibleWhen for menu contributions.
-The command framework provides the IEvaluationContext that command core expressions are evaluate against.
+The [Platform Command Framework](PlatformCommandFramework.md) uses [core expressions](Platform_Expression_Framework.md) for `enabledWhen` and `activeWhen` for handlers, programmatic activation of contexts, and for `visibleWhen` for menu contributions.
+The command framework provides the `IEvaluationContext` that command core expressions are evaluate against.
 
-The IEvaluationContext provides a default variable for evaluations, and a number of named variables.
+The `IEvaluationContext` provides a default variable for evaluations, and a number of named variables.
 In the command framework, we provide the global selection as a `java.util.Collection` as the default variable.
 It can either be empty, have one entry (if the ISelection was something like an ITextSelection), or have the contents of an IStructuredSelection.
 
-The <with/> element can be used to change which variable the child expression elements are evaluating against.
+The `<with/>` element can be used to change which variable the child expression elements are evaluating against.
 
 Variables and the Command Framework
 ===================================
@@ -25,7 +25,7 @@ Some of the variables may not be set, depending on the current application conte
 
 | Name | Type | Description | Since |
 | --- | --- | --- | --- |
-| activeContexts | A `java.util.Collection` of `java.lang.String` |   This is a collection of the active context IDs as strings. Most commonly used with <iterate/>, <count/>, and <test/> with a combined `org.eclipse.common.expressions.PropertyTester`. In **3.3** action sets are mirrored by contexts whose parent is `org.eclipse.ui.actionSet`, and the active action sets show up in the list of active contexts.   | 3.2 |
+| activeContexts | A `java.util.Collection` of `java.lang.String` |   This is a collection of the active context IDs as strings. Most commonly used with `<iterate/>`, `<count/>`, and `<test/>` with a combined `org.eclipse.common.expressions.PropertyTester`. In **3.3** action sets are mirrored by contexts whose parent is `org.eclipse.ui.actionSet`, and the active action sets show up in the list of active contexts.   | 3.2 |
 | activeActionSets | An `IActionSetDescriptor\[\]` |   **Note:** This is currently not used as it points to an internal class and the type might change in any release.   | 3.2 |
 | activeShell | `org.eclipse.swt.widgets.Shell` |   The currently active shell. It can be a dialog or workbench window shell.   | 3.2 |
 | activeWorkbenchWindowShell | `org.eclipse.swt.widgets.Shell` |   The active workbench window shell.   | 3.2 |
@@ -38,14 +38,15 @@ Some of the variables may not be set, depending on the current application conte
 | activePart | `org.eclipse.ui.IWorkbenchPart` |   The active part, which can be the same as the active editor.   | 3.2 |
 | activePartId | `java.lang.String` |   The ID of the currently active part.   | 3.2 |
 | activeSite | `org.eclipse.ui.IWorkbenchPartSite` |   The site of the currently active part.   | 3.2 |
-| selection | `org.eclipse.jface.viewers.ISelection` |   The current global selection. It is often used with <test/> elements with `org.eclipse.core.expressions.PropertyTester`, in programmatic core expressions, and in **3.3** with <iterate/> and <count/> elements.   | 3.2 |
-| activeMenu | A `java.util.Collection` of `java.lang.String` |   This is the list of IDs of the showing context menu. Examples are like #TextEditorRuler or a part ID. Most commonly used with <iterate/>, <count/>, and <test/> with a combined `org.eclipse.common.expressions.PropertyTester`.   | 3.2 |
+| org.eclipse.ui.selection | `Object` |   The current global selection if the `ESelectionService` is used. It is often used with `<test/>` elements with `org.eclipse.core.expressions.PropertyTester`, in programmatic core expressions, potentially with `<iterate/>` and `<count/>` elements.   | 4.0 |
+| selection | `org.eclipse.jface.viewers.ISelection` |   The current global selection. It is often used with `<test/>` elements with `org.eclipse.core.expressions.PropertyTester`, in programmatic core expressions, and in **3.3** with `<iterate/>` and `<count/>` elements.   | 3.2 |
+| activeMenu | A `java.util.Collection` of `java.lang.String` |   This is the list of IDs of the showing context menu. Examples are like #TextEditorRuler or a part ID. Most commonly used with `<iterate/>`, `<count/>`, and `<test/>` with a combined `org.eclipse.common.expressions.PropertyTester`.   | 3.2 |
 | activeMenuSelection | `org.eclipse.jface.viewers.ISelection` |   This is a selection that is available while a context menu is showing. It is the selection from the selection provider used to register the context menu, usually from `getSite().registerContextMenu(*)`. It is usually the same as the `selection`variable, but not always. This is more for legacy compatibility.   | 3.3 |
 | activeMenuEditorInput | `org.eclipse.jface.viewers.ISelection` |   This is a selection that is available while a context menu is showing. It is the selection from the editor input, usually if includeEditorInput was set to `true` during `getEditorSite().registerContextMenu(*)`. This is more for legacy compatibility.   | 3.3 |
 | activeFocusControl | `org.eclipse.swt.widgets.Control` |   A control that has focus and has been registered with the [IFocusService](https://github.com/eclipse-platform/eclipse.platform.ui/blob/master/bundles/org.eclipse.ui.workbench/eclipseui/org/eclipse/ui/swt/IFocusService.java).   | 3.3 |
 | activeFocusControlId | `java.lang.String` |   The ID of a control that has focus and has been registered with the `org.eclipse.ui.swt.IFocusService`.   | 3.3 |
 
-Note: All these variables can be used with <test/> and a `org.eclipse.common.expressions.PropertyTester`.
+Note: All these variables can be used with `<test/>` and a `org.eclipse.common.expressions.PropertyTester`.
 
 Property Testers
 ================
@@ -104,7 +105,7 @@ For example, to test an IResource name the property would be `org.eclipse.core.r
 | **Property** | **Description** |  |
 |   isPerspectiveOpen   |   Tests if any perspective is open.   |  |
 
-Expression examples
+Expression Examples
 ===================
 
 Here are some examples. I'll pretend all of the examples are deciding when a handler is active.
@@ -118,7 +119,7 @@ You can browse the [plugin.xml](https://github.com/eclipse-platform/eclipse.plat
 The InfoView provides an `IStructuredSelection` with 0 or more `org.eclipse.ui.examples.contributions.model.Person`.
 
 When using the default variable, you must treat it as an `java.util.Collection`.
-That means using <count> or <iterate>
+That means using `<count>` or `<iterate>`
 
 ```xml
     <activeWhen>
@@ -150,7 +151,7 @@ For example:
     </activeWhen>
 ```
 
-Active editor type
+Active Editor Type
 ------------------
 
 If you want your handler to be active for a specific type of editor, you can use **activeEditorId** to target your handler.
@@ -162,7 +163,7 @@ If you want your handler to be active for a specific type of editor, you can use
     </activeWhen>
 ```
 
-Complex nested boolean expressions
+Complex Nested Boolean Expressions
 ----------------------------------
 
 You can also write complex nested boolean expressions, like **(a & b & (c | d | (!e)))**:
@@ -188,16 +189,16 @@ New Core Expressions in 3.3
 
 In 3.3 there were 2 additions to the core expressions framework.
 
-count and iterate
+Count and Iterate
 -----------------
 
 Count and iterate have always worked against `java.util.Collection`.
-The <count/> and <iterate> elements can now be used on any variable that adapts to `org.eclipse.core.expressions.ICountable` and `org.eclipse.core.expressions.IIterable` or implements the interfaces directly.
+The `<count/>` and `<iterate>` elements can now be used on any variable that adapts to `org.eclipse.core.expressions.ICountable` and `org.eclipse.core.expressions.IIterable` or implements the interfaces directly.
 It wasn't possible to use the java 1.5 constructs for iterable.
 
 The workbench provides an adapter for `ISelection` and `IStructuredSelection`.
 
-definitions
+Definitions
 -----------
 
 The **org.eclipse.core.expressions.definitions** extension point was introduced.