Summary
-------

Document possible runtime vs compile-time difference in set of annotations present for  `RoundEnvironment.getElementsAnnotatedWith` methods taking a `Class` object.

Problem
-------

The set of annotation types available at runtime using `Class` objects may differ from the set of annotation types available at compile time using TypeElement objects. For example, the runtime class path may include type *not* on the compiler-type paths.

Solution
--------

Note this possibility in the affected methods.

Specification
-------------

    --- old/src/java.compiler/share/classes/javax/annotation/processing/RoundEnvironment.java	2018-11-02 09:55:44.074001000 -0700
    +++ new/src/java.compiler/share/classes/javax/annotation/processing/RoundEnvironment.java	2018-11-02 09:55:43.902001000 -0700
    @@ -143,11 +143,26 @@
          * simply because a {@code module-info} file for that module was
          * created.
          *
    +     * <p> Note: An implementation of this method typically performs
    +     * an internal conversion from the runtime reflective
    +     * representation of an annotation type as a {@code Class} object
    +     * to a different representation used for annotation
    +     * processing. The set of annotation types present in the runtime
    +     * context may differ from the set of annotation types present in
    +     * the context of annotation processing in a particular
    +     * environmental configuration. If an runtime annotation type is
    +     * not present in the annotation processing context, the situation
    +     * is not treated as an error and no elements are found for that
    +     * annotation type.
    +     *
          * @param a  annotation type being requested
          * @return the elements annotated with the given annotation type,
          * or an empty set if there are none
          * @throws IllegalArgumentException if the argument does not
          * represent an annotation type
    +     *
    +     * @see javax.lang.model.AnnotatedConstruct#getAnnotation(Class)
    +     * @see javax.lang.model.AnnotatedConstruct#getAnnotationsByType(Class)

          */
         Set<? extends Element> getElementsAnnotatedWith(Class<? extends Annotation> a);
     
    @@ -155,6 +170,18 @@
          * Returns the elements annotated with one or more of the given
          * annotation types.
          *
    +     * <p> Note: An implementation of this method typically performs
    +     * an internal conversion from the runtime reflective
    +     * representation of an annotation type as a {@code Class} object
    +     * to a different representation used for annotation
    +     * processing. The set of annotation types present in the runtime
    +     * context may differ from the set of annotation types present in
    +     * the context of annotation processing in a particular
    +     * environmental configuration. If an runtime annotation type is
    +     * not present in the annotation processing context, the situation
    +     * is not treated as an error and no elements are found for that
    +     * annotation type.
    +     *
          * @apiNote This method may be useful when processing repeating
          * annotations by looking for an annotation type and its
          * containing annotation type at the same time.
    @@ -172,6 +199,10 @@
          * @throws IllegalArgumentException if the any elements of the
          * argument set do not represent an annotation type
          * @jls 9.6.3 Repeatable Annotation Types
    +     *
    +     * @see javax.lang.model.AnnotatedConstruct#getAnnotation(Class)
    +     * @see javax.lang.model.AnnotatedConstruct#getAnnotationsByType(Class)
    +     *
          * @since 9
          */
         default Set<? extends Element> getElementsAnnotatedWithAny(Set<Class<? extends Annotation>> annotations){