Explicit notes on access to standard context beans in SpEL expressions

Closes gh-25037

spring-context/src/main/java/org/springframework/context/expression/StandardBeanExpressionResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -41,8 +41,13 @@ import org.springframework.util.StringUtils;
  * {@link org.springframework.beans.factory.config.BeanExpressionResolver}
  * interface, parsing and evaluating Spring EL using Spring's expression module.
  *
+ * <p>All beans in the containing {@code BeanFactory} are made available as
+ * predefined variables with their common bean name, including standard context
+ * beans such as "environment", "systemProperties" and "systemEnvironment".
+ *
  * @author Juergen Hoeller
  * @since 3.0
+ * @see BeanExpressionContext#getBeanFactory()
  * @see org.springframework.expression.ExpressionParser
  * @see org.springframework.expression.spel.standard.SpelExpressionParser
  * @see org.springframework.expression.spel.support.StandardEvaluationContext

src/docs/asciidoc/core/core-expressions.adoc

@@ -539,8 +539,12 @@ example shows:
 	</bean>
 ----
 
-The `systemProperties` variable is predefined, so you can use it in your expressions, as
-the following example shows:
+All beans in the application context are available as predefined variables with their
+common bean name. This includes standard context beans such as `environment` (of type
+`org.springframework.core.env.Environment`) as well as `systemProperties` and
+`systemEnvironment` (of type `Map<String, Object>`) for access to the runtime environment.
+
+The following example shows access to the `systemProperties` bean as a SpEL variable:
 
 [source,xml,indent=0,subs="verbatim"]
 ----
@@ -551,8 +555,7 @@ the following example shows:
 	</bean>
 ----
 
-Note that you do not have to prefix the predefined variable with the `#`
-symbol in this context.
+Note that you do not have to prefix the predefined variable with the `#` symbol here.
 
 You can also refer to other bean properties by name, as the following example shows:
 
@@ -576,8 +579,8 @@ You can also refer to other bean properties by name, as the following example sh
 [[expressions-beandef-annotation-based]]
 === Annotation Configuration
 
-To specify a default value, you can place the `@Value` annotation on fields, methods, and method or constructor
-parameters.
+To specify a default value, you can place the `@Value` annotation on fields, methods,
+and method or constructor parameters.
 
 The following example sets the default value of a field variable: