What does this do? Shader Language

I am learning shader language and I was curious, what does this do “float4(float3(0.0),1.f)”? This is not exact Unity syntax but I want to understand what float4(float3()) does.

float3(0.0) will set all three xyz elements to 0.0. This is just a shorter way of typing float3(0.0, 0.0, 0.0).
So the float4’s xyz is being set to 0.0, and the last w is being set to 1.0