wp-includes/formatting.php:2782Adds backslashes before letters and before a number at the start of a string.
$valuestringstringfunction backslashit( $value ) { if ( isset( $value[0] ) && $value[0] >= '0' && $value[0] <= '9' ) { $value = '\\\\' . $value; } return addcslashes( $value, 'A..Za..z' );}Introduced in 0.71. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/formatting.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.