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docs/building/internals.md

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+Internals of build process
+=========================================
+
+The purpose of this document is to explain build process **internals** with subtle nuances. 
+This document is not by any means complete.
+The ultimate source of truth is the code in `.\build.psm1` that's getting executed on the corresponding CI system.
+
+This document assumes, that you can successfully build PowerShell from sources for your platform.
+
+
+Top directory
+-----------
+
+We are calling `dotnet` tool build for `$Top` directory
+
+- `src\powershell` for CoreCLR builds (all platforms)
+- `src\Microsoft.PowerShell.ConsoleHost` for FullCLR builds (Windows only)
+
+Modules
+----------
+
+There are 3 modules directories with the same purpose: they have **content** files (i.e. `*.psm1`, `*.psd1`)
+which would be binplaced by `dotnet`
+
+- `src\Modules` shared between all flavours
+- `src\Microsoft.PowerShell.ConsoleHost\Modules` FullCLR (Windows)
+- `src\powershell\Modules` CoreCLR (all platforms)