SONARJAVA-4200 Fixes from review

* Change property value description
* Add missing "of"

java-frontend/src/main/java/org/sonar/java/SonarComponents.java

@@ -87,8 +87,9 @@ public class SonarComponents {
   public static final String SONAR_BATCH_SIZE_KEY = "sonar.java.experimental.batchModeSizeInKB";
   public static final String SONAR_FILE_BY_FILE = "sonar.java.fileByFile";
   /**
-   * Enables optimized analysis of unchanged by skipping some checks.
-   * Defaults to true.
+   * Describes if an optimized analysis of unchanged by skipping some rules is enabled.
+   * By default, the property is not set (null), leaving SQ/SC to decide whether to enable this behavior.
+   * Setting it to true or false, forces the behavior from the analyzer independently of the server.
    */
   public static final String SONAR_CAN_SKIP_UNCHANGED_FILES_KEY = "sonar.java.skipUnchanged";
 

sonar-java-plugin/src/main/resources/static/documentation.md

@@ -78,12 +78,12 @@ In practice, this means that on a file that has not changed, the analyzer only r
 To get a better understanding of the rule exclusion mechanism, keep in mind that:
 * Rules that need to run on multiple files to decide whether they need to raise issues are always executed
 * Rules that need to run at the end of the analysis to decide whether they need to raise issues are always executed
-* Rules that are defined out of the `sonar.java.checks` package are always executed
+* Rules that are defined outside of the `sonar.java.checks` package are always executed
 
 This last criteria implies that [custom rules](https://redirect.sonarsource.com/doc/java-custom-rules-guide.html) cannot be skipped.
 
 If you wish to disable this optimization, you can set the value of the analysis parameter `sonar.java.skipUnchanged` to `false`.
-Leaving the parameter untouched is equivalent to having `sonar.java.skipUnchanged` set to `true`.
+Leaving the parameter unset lets the server decide whether the optimization should be enabled.
 
 ## Analyzing JSP and Thymeleaf for XSS vulnerabilities