Only the claims define the power to block others from using the ideas in the patent. In theory. But remember that the patentee (that's the one with the patent

Only the claims define the power to block others from using the ideas in the patent. In theory. But remember that the patentee (that's the one with the patent) can always keep a "continuation" pending. With a continuation, the patentee can rewrite the claims however he wants. He can wait until your product is on the market and rewrite his claims to follow your product exactly. He could even sue you, lose for invalidity or noninfringement, and then rewrite his claims to more closely match your product and sue you again. The only limit on claim rewriting is that the new claims have to somewhat reflect what's in the specification and have to be reexamined. Reexamination, like examination, is more a coin flip than an engineering evaluation of the patent claims. Reflecting the specification doesn't have to follow too closely what was in there originally but it does place some limit on the breadth of claim rewriting. And rewritten claims have the same long ago priority date against prior art as the original claims. Your product does not count as prior art just because it was widely known when the new claims are written.