It has taken over a month for sellers to mount a high volume challenge, but today was one such day. In terms of total volume, it was one of the worst days for 2013. And in the context of the rally, it offers a sign for a potential swing high, but doesn't break the larger bullish trend - it will take much more selling to do that.
The Nasdaq did lose the tightly ascending support line established from the April swing low. A move to the 20-day MA looks most likely.
The mini-rally started in mid-April continued to rule the roost. Today's low volume losses continued with the trend which has supported the rally: namely high volume gains, and low volume losses.
The S&P sits 12% above its 200-day MA, which is unusually high. Although the S&P has managed to rally to 20% above its 200-day MA; typically this is done after a major low, and not at the latter stages of an advance. Neither action in the indices or supporting technicals suggest this rally is about to end soon.
Small Caps got a key uptick against the Nasdaq after two months of underperformance, although the Russell 2000 continued to lag against the S&P. However, today was important day for re-establishing the importance of Small Caps as a component of the broader rally. No rally can sustain itself for long periods without the participation of the Russell 2000.