S&P 500 Healthy But There Are Concerns, StockCharts.com's Keller Says

The video discusses the current state of the stock market, focusing on the S&P 500 chart. It highlights the market's upward trend, noting the overbought RSI and the decreasing number of stocks above the 50-day moving average. Concerns about small and mid cap participation are addressed, with a positive outlook on their performance if they maintain an uptrend.

What concerns were raised regarding the percentage of S&P stocks above their 50-day moving average?

What does the phrase 'stairs up' imply about the market trend discussed?