Why the pom for jsf-impl does not contain a dependency to jsf-api

Why the pom for jsf-impl does not contain a dependency to jsf-api

References

Reference NO 1

http://stackoverflow.com/questions/15561352/what-is-the-difference-between-javax-faces-2-1-14-jar-from-jsf-api-2-2-0-m05-jar

Reference NO 2

http://stackoverflow.com/questions/3234898/maven-problem-missing-artifact-jsf-api-jar

Reference NO 3

https://community.jboss.org/thread/228085

Reference NO 4

http://www.icesoft.org/JForum/posts/list/19931.page

Reference NO 5

http://www.mkyong.com/jsf2/primefaces/primefaces-hello-world-example/

Reference NO 6

http://www.tutorialspoint.com/jsf/jsf_quick_guide.htm

Reference NO 7

http://maxheapsize.com/2009/07/03/getting-started-with-jsf-2-and-maven

Reference NO 8

http://javaserverfaces.java.net/download.html