diff --git a/lib/system.nim b/lib/system.nim
index e2d214ef0..442686c07 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -3286,14 +3286,19 @@ when declared(initDebugger):
 when hasAlloc:
   # XXX: make these the default (or implement the NilObject optimization)
   proc safeAdd*[T](x: var seq[T], y: T) {.noSideEffect.} =
+    ## Adds ``y`` to ``x`` unless ``x`` is not yet initialized; in that case, 
+    ## ``x`` becomes ``@[y]``
     if x == nil: x = @[y]
     else: x.add(y)
 
   proc safeAdd*(x: var string, y: char) =
+    ## Adds ``y`` to ``x``. If ``x`` is ``nil`` it is initialized to ``""``
     if x == nil: x = ""
     x.add(y)
 
   proc safeAdd*(x: var string, y: string) =
+    ## Adds ``y`` to ``x`` unless ``x`` is not yet initalized; in that case, ``x``
+    ## becomes ``y``
     if x == nil: x = y
     else: x.add(y)