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doc/posix_pipe.md

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+# POSIX Piped Input in FTXUI
+
+## What is a POSIX Pipe?
+
+A POSIX pipe is a way for two separate programs to communicate. One program sends its output directly as input to another program. Think of it like a one-way tube for data.
+
+**Example:**
+
+Imagine you want to list files and then filter them interactively.
+
+- `ls`: Lists files.
+- `interactive_grep`: An FTXUI application that filters text and lets you type.
+
+You can connect them with a pipe (`|`):
+
+```bash
+ls -l | interactive_grep
+```
+
+Here's what happens:
+1. `ls -l` lists files with details.
+2. The `|` sends this list directly to `interactive_grep`.
+3. `interactive_grep` receives the list and displays it. Because it's an FTXUI app, you can then type to filter the list, even though it received initial data from `ls`.
+
+## How FTXUI Handles Piped Input
+
+Now that you understand what a POSIX pipe is, let's look at how FTXUI uses them.
+
+FTXUI lets your application read data from other programs (like from a pipe) while still allowing you to use your keyboard for interaction. This is useful for interactive command-line tools that process data.
+
+Normally, FTXUI applications receive all input from `stdin`. However, when FTXUI detects that `stdin` is connected to the output of a pipe (meaning data is being piped into your application), it automatically switches to reading interactive keyboard input from `/dev/tty`. This ensures that your application can still receive user input even while processing piped data.
+
+This feature is **turned on by default**.
+
+If your FTXUI application needs to read piped data and also respond to keyboard input, you typically don't need to do anything special:
+
+```cpp
+auto screen = ScreenInteractive::Fullscreen();
+// screen.HandlePipedInput(true); // This is enabled by default
+screen.Loop(component);
+```
+
+**Note:** This feature works only on Linux and macOS. It does nothing on Windows.
+
+## Turning Off Piped Input
+
+If you don't need this feature, or if it conflicts with your custom input handling, you can turn it off.
+
+To disable it, call `HandlePipedInput(false)` before starting your application's main loop:
+
+```cpp
+auto screen = ScreenInteractive::Fullscreen();
+screen.HandlePipedInput(false); // Turn off piped input handling
+screen.Loop(component);
+```