sgf-parsing: Replace incorrect info with correct info (#2114)

* sgf-parsing: improve description flow

There is a bit of opinion on what makes better flow. The main opinion
of this commit:

High-level description of the goal should come earlier; that way the
high-level goal can be kept in mind when reading the details below.

So two pieces of text are moved:

First, the overall goal of the exercise.
Second, that all property values are Text.

* sgf-parsing: Replace incorrect info with correct info

285d2e6 added outright incorrect info
("Incorrect" means it violates the specification found at
https://www.red-bean.com/sgf/sgf4.html#text).

It is replaced with correct info. As follows:

* Newlines are treated differently based on whether they come after a \
* SGF does **not** have escape sequences for whitespace characters, so
  it doesn't make sense to talk about escaped forms for them.
* There is no need or expectation for parentheses or semicolons to be
  escaped, so remove the sentence about that.

All statements in this commit are already being tested by tests added in
3c33c24, so no additional tests need be
added.

Co-authored-by: Katrina Owen <[email protected]>

Author: petertseng

exercises/sgf-parsing/description.md

@@ -9,6 +9,8 @@ tree of nodes where each node is a property list. The property list
 contains key value pairs, each key can only occur once but may have
 multiple values.
 
+The exercise will have you parse an SGF string and return a tree structure of properties.
+
 An SGF file may look like this:
 
 ```text
@@ -52,17 +54,16 @@ A key can have multiple values associated with it. For example:
 
 Here `AB` (add black) is used to add three black stones to the board.
 
-According the the SGF specification `\` is the escape character. When `\` is
-encountered during parsing, it indicates that the following character should be
-printed as is. The exception to this is whitespace, with newline, carriage
-return and tab encoded as `"\n"`, `"\r"` and `"\t"` respectively. When parsing
-you can expect some characters to _always_ be escaped, including parentheses,
-square brackets, semicolons and colons.
+All property values will be the [SGF Text type][sgf-text].
+You don't need to implement any other value type.
+Although you can read the [full documentation of the Text type][sgf-text], a summary of the important points is below:
 
-When parsing SGF files whitespace gets special handling, with the exception of
-newlines any whitespace character encountered is replaced with a single space
-character irrespective of if the original character is found in its escaped
-from or its unescaped from.
+- Newlines are removed if they come immediately after a `\`, otherwise they remain as newlines.
+- All whitespace characters other than newline are converted to spaces.
+- `\` is the escape character.
+  Any non-whitespace character after `\` is inserted as-is.
+  Any whitespace character after `\` follows the above rules.
+  Note that SGF does **not** have escape sequences for whitespace characters such as `\t` or `\n`.
 
 Be careful not to get confused between:
 
@@ -78,10 +79,5 @@ that. Furthermore you may assume that all newlines are unix style (`\n`,
 no `\r` or `\r\n` will be in the tests) and that no optional whitespace
 between properties, nodes, etc will be in the tests.
 
-The exercise will have you parse an SGF string and return a tree
-structure of properties. You do not need to encode knowledge about the
-data types of properties, just use the rules for the
-[text][sgf-text] type everywhere.
-
 [sgf]: https://en.wikipedia.org/wiki/Smart_Game_Format
 [sgf-text]: http://www.red-bean.com/sgf/sgf4.html#text