document will_render better

diff --git a/doc/plugins/write.mdwn b/doc/plugins/write.mdwn
index 77f336dca01ad966a09f8e9c461ab0df82100b48..0e1839c6ca31157ddf0b5edcfd4d78529fbb2327 100644 (file)
--- a/doc/plugins/write.mdwn
+++ b/doc/plugins/write.mdwn
@@ -449,6 +449,10 @@ destination directory), register that the page will result in that file
 being rendered. It's important to call this before writing to any file in
 the destination directory.
 
+Ikiwiki uses this information to automatically clean up rendered files when
+the page that rendered them goes away or is changes to no longer render
+them. will_render also does a few important security checks.
+
 #### `pagetype($)`
 
 Given the name of a source file, returns the type of page it is, if it's