The secrets that might be in Uber's S-1 filing

One intriguing thing to look for in Uber's S-1, whenever it arrives, is how much information it provides about the other ride-hail companies in which it holds shares.

The bottom line: These holdings, particularly in China's Didi Chuxing, could represent a sizable percentage of Uber's proposed market cap. Investors are going to want more than just the latest VC valuations. This also could be where Uber benefits a bit from an IPO for Lyft — assuming it doesn't get taken out first, Qualtrics-style — in that there will be another third-party data point.

Go deeper: Breaking down the Uber-Lyft-Slack IPO rush