diff --git a/src/lib.rs b/src/lib.rs
index b2819a7..67c567f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1 +1 @@
-pub mod parser;
\ No newline at end of file
+pub mod parser;
diff --git a/src/parser.rs b/src/parser.rs
index c40a4d1..18620a3 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -3,6 +3,7 @@ use colorful::*;
 use rand::prelude::*;
 use std::fs::*;
 use std::iter::repeat_with;
+const CONTROLS: [char; 3] = ['\n', '\r', '\t'];
 #[derive(Clone, Debug)]
 pub struct Parser {
     pub file: Option<String>,
@@ -25,7 +26,7 @@ impl Parser {
         }
     }
     pub fn next_token(&mut self) -> Option<Vec<&str>> {
-        if self.position == (self.context.len() - 1) {
+        if (self.position) >= (self.context.len() - 1) {
             return None;
         }
         let substr: &str = self
@@ -45,8 +46,8 @@ impl Parser {
                 .collect::<Vec<&str>>(),
         )
     }
-    fn is_vailid_token(&self, token: &str) -> bool {
-        self.parse(vec![token]).is_ok() || token.parse::<f64>().is_ok()
+    pub fn is_vailid_token(&self, token: &str) -> bool {
+        self.parse(vec![token]).is_ok() || token.parse::<f64>().is_ok() || CONTROLS.iter().any(|&x| token.contains(x))
     }
     pub fn parse(&self, tokens: Vec<&str>) -> Result<String> {
         if tokens.len() != 1 {
@@ -73,11 +74,15 @@ impl Parser {
                         .collect::<String>()
                 });
             }
-            "string" => Ok(
-                repeat_with(|| thread_rng().gen_range(10_u8..126_u8) as char)
-                    .take(random::<u16>() as usize)
-                    .collect::<String>(),
-            ),
+            "string" => Ok(repeat_with(|| {
+                if random::<u16>() % 26 == 0 {
+                    CONTROLS[thread_rng().gen_range(0..=2)]
+                } else {
+                    thread_rng().gen_range(32_u8..=126_u8) as char
+                }
+            })
+            .take(random::<u16>() as usize)
+            .collect::<String>()),
             "char" => Ok(random::<char>().to_string()),
             _ => bail!(
                 "{}",
@@ -105,19 +110,20 @@ impl Parser {
                         )
                         .to_string());
                 }
-                _ => {
-                    if !self.is_vailid_token(i) {
-                        ret = Err(anyhow!(
-                            "{}",
-                            format!(
-                                "failed to parse at position {} : read undeclared tokens",
-                                self.position + 1
-                            )
-                            .color(Color::Red)
-                            .bold()
-                        ));
+                "contains" => {
+                    if tokens[0] != "string" {
+                        ret = Err(anyhow!("{}\n{}",format!("Parse error at position {} : unable to confine `contains` for current type",self.position + 1).color(Color::Red).bold(),"note : the multi token `contains` is only valid for type string".color(Color::Blue)));
+                    } else {
+                        let mut str = self.parse(vec!["string"]).unwrap();
+                        if !str.contains(tokens[c + 1]) {
+                            str.insert_str(thread_rng().gen_range(0..str.len()), tokens[c + 1]);
+                        }
+                        ret = Ok(str);
                     }
                 }
+                _ => {
+                    
+                }
             }
         }
         ret