Difference between current(), node() and self ??

Until now, I thought that
<xsl:value-of select="self"/>, <xsl:value-of select="node()"/> and
<xsl:value-of select="current()"/> would print out the same values,
but found out that this is not true.

It seems that current() prints out all the values including its child...
and node() and self... could anyone please tell me what exactly the
difference between these?

Thank you!
-Jaebin