fix(stdlib): make IS_NUM agree with STR_TO_NUM and explain conversion errors

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/doc/language/function/cpsc-function-str_to_num.7.md b/doc/language/function/cpsc-function-str_to_num.7.md
index acdf60b..48d24db 100644
--- a/doc/language/function/cpsc-function-str_to_num.7.md
+++ b/doc/language/function/cpsc-function-str_to_num.7.md
@@ -14,7 +14,7 @@ STR_TO_NUM(text : STRING) RETURNS REAL
 
 Provided by the standard string library, loaded and linked by default.
 
-Return REAL, including for integer-looking text. The whole string must be consumed. Invalid text, trailing junk and values outside the REAL range throw a catchable exception. Use IS_NUM first to check numeric text without throwing for invalid input.
+Return REAL, including for integer-looking text. The whole string must be consumed. Invalid text and trailing junk throw a catchable exception reading `STR_TO_NUM: '<text>' is not a number`, and overflowing values throw `STR_TO_NUM: '<text>' is out of the REAL range`. Underflow is accepted. Use IS_NUM first to check numeric text without throwing for invalid input.
 
 # EXAMPLE