According to 'man readline':
Readline has variables that can be used to further customize its behavior. A
variable may be set in the inputrc file with a statement of the form
set variable-name value
Except where noted, readline variables can take the values On or Off (without
regard to case). Unrecognized variable names are ignored. When a variable
value is read, empty or null values, "on" (case-insensitive), and "1" are
equivalent to On. All other values are equivalent to Off. The variables and
their default values are:
(...)
isearch-terminators (``C-[ C-J'')
The string of characters that should terminate an incremental search without
subsequently executing the character as a command. If this variable has not
been given a value, the characters ESC and C-J will terminate an incremental
search.
