doc/tutorial/basics: various improvements
- added section for templates
- updated ambiguity in bottom.md
- several small fixes
Change-Id: Iac03e7b99eec1ea352cb30d815a8cfbfb6896b18
diff --git a/doc/tutorial/basics/bottom.md b/doc/tutorial/basics/bottom.md
index 6a6ac5d..77be74b 100644
--- a/doc/tutorial/basics/bottom.md
+++ b/doc/tutorial/basics/bottom.md
@@ -1,15 +1,16 @@
[TOC](Readme.md) [Prev](duplicates.md) [Next](types.md)
-_Types and Values_
+_Types ~~and~~ are Values_
# Bottom
-Specifying duplicate fields with conflicting values results in an error,
-denoted `_|_`.
-
-Technically speaking, bottom is just a value like any other.
-But for all practical purposes it is okay to think of the bottom value
-as an error.
+Specifying duplicate fields with conflicting values results in an error
+or bottom.
+_Bottom_ is a special value in CUE, denoted `_|_`, that indicates an
+error such as incompatible values.
+Any error in CUE results in `_|_`.
+Logically all errors are equal, although errors may be associated with
+metadata such as an error message.
Note that an error is different from `null`: `null` is a valid JSON value,
whereas `_|_` is not.
@@ -21,10 +22,15 @@
l: [ 1, 2 ]
l: [ 1, 3 ]
+
+list: [0, 1, 2]
+val: list[3]
```
<!-- result -->
```
-a: _|_
-l: _|_
+a: _|_
+l: _|_
+list: [0, 1, 2]
+val: _|_
```
\ No newline at end of file
