doc: Add some general documentation about negated options

Author: ryanofsky

doc/bitcoin-conf.md

@@ -8,6 +8,16 @@ Changes to the configuration file while `bitcoind` or `bitcoin-qt` is running on
 
 Users should never make any configuration changes which they do not understand. Furthermore, users should always be wary of accepting any configuration changes provided to them by another source (even if they believe that they do understand them).
 
+## Configuration File Precedence
+
+Options specified in the configuration file can be overridden by options in the [`settings.json` file](files.md) and by options specified on the command line.
+
+The `settings.json` file contains dynamic settings that are set by the Bitcoin Core GUI and RPCs at runtime, and augment or replace the static settings specified in the `bitcoin.conf` file.
+
+Command line options also augment or replace `bitcoin.conf` options, and can be useful for scripting and debugging.
+
+It is possible to see which setting values are in use by checking `debug.log` output. Any unrecognized options that are found in `bitcoin.conf` also show up as warnings in `debug.log` output.
+
 ## Configuration File Format
 
 The configuration file is a plain text file and consists of `option=value` entries, one per line. Leading and trailing whitespaces are removed.
@@ -49,6 +59,14 @@ regtest.rpcport=3000
 rpcport=4000
 ```
 
+### Negated options
+
+Almost all options can be negated by being specified with a `no` prefix. For example an option `-foo` could be negated by writing `nofoo=1` or `nofoo=` in the configuration file or `-nofoo=1` or `-nofoo` on the command line.
+
+In general, negating an option is like setting it to `0` if it is a boolean or integer option, and setting it to an empty string or path or list if it is a string or path or list option.
+
+However, there are exceptions to this general rule. For example, it is an error to negate some options (e.g. `-nodatadir` is disallowed), and some negated strings are treated like `"0"` instead of `""` (e.g. `-noproxy` is treated like `-proxy=0`), and some negating some lists can have side effects in addition to clearing the lists (e.g. `-noconnect` disables automatic connections in addition to dropping any manual connections specified previously with `-connect=<host>`). When there are exceptions to the rule, they should either be obvious from context, or should be mentioned in usage documentation. Nonobvious, undocumented exceptions should be reported as bugs.
+
 ## Configuration File Path
 
 The configuration file is not automatically created; you can create it using your favorite text editor. By default, the configuration file name is `bitcoin.conf` and it is located in the Bitcoin data directory, but both the Bitcoin data directory and the configuration file path may be changed using the `-datadir` and `-conf` command-line options.