--- a/NEWS Sat Nov 20 20:42:41 2021 +0100
+++ b/NEWS Sun Nov 21 17:42:11 2021 +0100
@@ -548,17 +548,21 @@
INCOMPATIBILITY: HTTP proxy configuration now works via JVM properties
https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/net/doc-files/net-properties.html
+* System options may declare an implicit standard value, which is used
+when the option is activated without providing an explicit value, e.g.
+"isabelle build -o document -o document_output" instead of
+"isabelle build -o document=true -o document_output=output". For options
+of type "bool", the standard is always "true" and cannot be specified
+differently.
+
+* System option "document=true" is an alias for "document=pdf", and
+"document=false" is an alias for "document=" (empty string).
+
* System option "system_log" specifies an optional log file for internal
-messages produced by Output.system_message in Isabelle/ML; the value
-"true" refers to console progress of the build job. This works for
+messages produced by Output.system_message in Isabelle/ML; the standard
+value "-" refers to console progress of the build job. This works for
"isabelle build" or any derivative of it.
-* System options of type string may be set to "true" using the short
-notation of type bool. E.g. "isabelle build -o system_log".
-
-* System option "document=true" is an alias for "document=pdf" and thus
-can be used in the short form. E.g. "isabelle build -o document".
-
* Command-line tool "isabelle version" supports repository archives
(without full .hg directory). It also provides more options.