Created SC1123 (markdown)

SC1123.md

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+## ShellCheck directives are only valid in front of complete compound commands, like `if`, not e.g. individual `elif` branches.
+
+### Problematic code:
+
+```sh
+if [ "$prod" = "true" ]
+then
+  echo "Prod mode"
+# shellcheck disable=2154
+elif [ "$debug" = "true" ]
+then
+  echo "Debug mode"
+fi
+```
+
+### Correct code:
+```sh
+# Applies to entire `if...fi` command
+# shellcheck disable=2154
+if [ "$prod" = "true" ]
+then
+  echo "Prod mode"
+elif [ "$debug" = "true" ]
+then
+  echo "Debug mode"
+fi
+```
+
+or 
+
+```sh
+if [ "$prod" = "true" ]
+then
+  echo "Prod mode"
+elif  # Applies only to this [ .. ] command
+      # shellcheck disable=2154
+      [ "$debug" = "true" ]
+then
+  echo "Debug mode"
+fi
+```
+
+
+### Rationale:
+
+You appear to have put a directive before a non-command keyword, such as `elif`, `else`, `do`, `;;` or similar. 
+
+Unlike many other linters, ShellCheck comment directives apply to the next shell command, rather than to the next line of text.
+
+This means that you can put a directive in front of a `while` loop, `if` statement or function definition, and it will apply to that entire structure.
+
+However, it also means that you can not apply the directive to non-commands like an individual `elif` or `else` block since these are not commands by themselves, and rather just parts of an `if` compound command.
+
+Please move the directive in front of the nearest applicable command that contains the code you want to apply it to, such as before the `if`. 
+
+### Exceptions:
+
+None.