add divergences section to README.md and fixed reversed and noop arguments

README.md

@@ -11,3 +11,28 @@ npm run parser-test      # run the corpus tests in test/corpus
 npm run parser-build     # build the WASM binary
 npm run playground       # interactively explore the grammar
 ```
+
+## Divergences from Django
+
+The grammar aims to accept what Django accepts, with one deliberate exception. Where Django takes an
+input without complaint but the input is almost certainly a mistake — it parses, and then silently
+renders nothing or quietly ignores half of what was written — the grammar reports an error instead.
+Every case below is input Django itself accepts:
+
+- **Number-shaped names.** Django has no number token: a word is a literal if `int()` or `float()` parses
+  it and a variable lookup otherwise, so `0x1f`, `1a`, `1.`, `1.2.3` and `1__0` look up a variable of that
+  name and render nothing.
+- **An attribute of `True`, `False` or `None`.** Every Django context is seeded with those three names, so
+  `{{ True.x }}` is an ordinary two-part lookup that can never resolve.
+- **A keyword argument written twice.** `{% with a=1 a=2 %}`, and the same in `{% include %}` and
+  `{% blocktranslate %}`, where Django builds a dict and lets the last value win.
+- **Anything after a `{% static %}` path.** `StaticNode.handle_token` looks for `as` two words from the end
+  and ignores the rest, so `{% static "a" junk %}` and `{% static "a" as url junk %}` render as if the
+  extra words were not there.
+- **A `{% cache %}` argument meant as something other than the fragment name.** Django takes the raw word
+  in that position, so `{% cache 500 using="c" %}` names a fragment called `using="c"` rather than choosing
+  a cache, and `{% cache 500 sidebar.name %}` names one with a dot in it.
+
+In the other direction the grammar is more permissive only where it cannot know better: the names a
+`{% load %}` brings in live in Python, so `{{ x|lenght }}` cannot be told from a filter some library
+registered, and an unknown tag's arguments are assumed to have the shape `simple_tag` gives them.