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+A style guide is a list of decisions we've made, that we want to be consistent
+about going forwards. It does not need to be comprehensive of all possible
+issues, nor does it need to confine itself to trivial topics such as
+formatting. It's a tool for ourselves so we don't forget where we've been, and
+can avoid solving the same problems again.
+
+If you're collaborating with us on something, don't be shy about adding to
+this guide. Things written here do impose some burden, but the hope is that
+they lessen other burdens in the long run. Use your judgement about what's
+worth it.
+
+Please fix style issues in existing code as you encounter them. Style is
+aspirational, a journey not a destination. :)
+
diff --git a/Rust.md b/Rust.md
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+# Whitespace
+
+## Indentation
+
+Use two-space indentation for any form of block nesting:
+
+```
+fn command_str(c: char, state: &mut RPState) -> Result<(), Exit> {
+  if c != ')' {
+    state.wip_str.push(c);
+  }
+}
+```
+
+
+## Line wrapping
+
+To the greatest extent possible, never have a line wider than 80 characters.
+
+If you can, break long statements into shorter ones. If you can't, wrap them
+onto multiple lines. There are two ways to do this.
+
+EITHER indent by four spaces with respect to the parent line:
+
+```
+              return Err(err_msg(format!(
+                  "Stack depth should be at least: {}", d)));
+```
+
+OR indent to a depth that lines up with the start of the sub-expression you're
+breaking in:
+
+```
+    state.num += to_decimal(c.to_digit(10).unwrap())
+                 * state.decimal_offset;
+```
+
+When doing the latter, put any operator or other punctuation that's needed
+at the beginning of the continuation line, not the end of the first line.
+
+In very rare situations when the structure of code is some sort of tabular
+list, it may make sense to break with these patterns and indent in ways that
+make the tabular structure evident.
+
+Regardless of which type of continuation line you choose, if the line you're
+wrapping is also the start of a block, put the curly brace or similar
+block-opening character on a line by itself:
+
+```
+  } else if let 'p' | 'n' | 'q' | 'l' | 's' | 'v' | 'x' | 'd' | ',' | 'c'
+              | '!' | '?' = c
+  {
+```
+
+Notice that this example also happens to demonstrate the tabular-structure
+approach.
+
+
+## Indent or wrap?
+
+Because Rust does the thing where control flow constructs and compound
+literals are ordinary expressions that can be used anywhere, you may sometimes
+have to apply some judgement about whether to treat a piece of code as a block
+or a continued line.
+
+In this example, an array literal is being treated as a code block:
+
+```
+  let kvs = [
+    ("F->C", "1! 32- 5 9/*"),
+    ("C->F", "1! 9 5/* 32+"),
+    ("C->K", "1! 273+"),
+    ("K->C", "1! 273-"),
+    ("Km->mi", "1! 1.609344/"),
+    ("mi->Km", "1! 1.609344*"),
+  ].map(|kv: (&str, &str)| (String::from(kv.0), Value::Str(kv.1.into())));
+```
+
+
+## Vertical space at the top level
+
+In general, put two blank lines between function or type definitions that are
+unrelated to each other.
+
+If you wish to express that two top-level constructs are closely related, such
+as a trait implementation definition or utility function immediately following
+a type definition that it pertains to, use a single blank line instead of two.
+
+Constant definitions may directly abut each other - with no intervening
+lines - if you so wish.
+
+Put all `use` and `mod` declarations at the top of the file, with two blank
+lines separating this section from everything else the file defines.
+