double sel0 = mProject->GetSel0();In this example, the sel0 variable is declared as a double, and its value is set by calling the GetSel0() method on the mProject object. This function is part of the Audacity API and is included in the "audacity" package library. It is commonly used in Audacity plugin development to create custom effects or tools that operate on the selected portion of an audio track. Overall, the GetSel0 function provides a simple and straightforward way to access the start time of a user-selected region in an Audacity project.