What is the difference between 'diff3' and 'svn merge' commands?

Is there any difference between the algorithm of how diff3 utility and svn merge commands work? Does svn merge use the same principle or some variation of how diff3 works? For example, diff3 does not automatically merge changes if mine and theirs files have th开发者_如何学编程e same content while svn up or svn merge does.

My question is also closely related to the automatic merging. How does it work? When conflict happens and when it does not? It's obvious that conflict happens when the same lines of source code have been edited, but there are cases when it is impossible to define merge context? How svn merge defines it?

I've found following passage at the 'Copying Changes Between Branches' page from svn book:

...svn diff only outputs the limited patch-format, so there are some ideas it simply can't express. The svn merge command, however, can express tree-changes by directly applying them to your working copy

What are all those differences? I cannot find detailed info anywhere.

Difference is that svn merge command can express tree-changes while svn diff can not. Detailed answer can be found after deep analysis of svn source code.