* Parse an expression.
*
* @param expr a pointer where is put an AVExpr containing the parsed
- * value in case of successfull parsing, or NULL otherwise.
+ * value in case of successful parsing, or NULL otherwise.
* The pointed to AVExpr must be freed with av_expr_free() by the user
* when it is not needed anymore.
* @param s expression as a zero terminated string, for example "1+2^3+5*5+sin(2/3)"