Info-search-whitespace-regexp is a variable defined in `info.el'.
Its value is

If non-nil, regular expression to match a sequence of whitespace chars.
This applies to Info search for regular expressions.
You might want to use something like "[ \t\r\n]+" instead.
In the Customization buffer, that is `[' followed by a space,
a tab, a carriage return (control-M), a newline, and `]+'.

You can customize this variable.