The <canvas> tag supports all of the normal line attributes (width, join style, cap style, miter limit) except for dashes. Given that Apple's original implementation of <canvas> seemed a little bit rushed, I have always assumed that this was a simple oversight, and that it would soon be corrected in newer implementations.
I did, however, submit a comment about it to WHAT-WG. I was quite surprised to find out that they have no intention of supporting dashed lines. I've argued and argued with Ian Hickson about this, but he is unmoved. Supporting dashed lines would be non-trivial, he believes, and there haven't been enough requests for them.
So, this post is a public service announcement. If you were assuming, as I did, that dashed lines would be supported by the official specification of the <canvas> tag, you should be aware that they will not be. If, like me, you think that it is a mistake to define a graphics library that cannot natively draw dashed lines, then you can submit a comment to that effect to whatwg@whatwg.org.
