Question: I am going through bootstrap's less code. I am curious what do '>' and '&' mean in defining css class?

```
  .navbar-nav {                                                                           
    > li > a {                                                                            
      color: @navbar-custom-link-color;                                                   

      &:hover,                                                                            
      &:focus {                                                                           
        color: @navbar-custom-link-hover-color;                                           
      }                                                                                   
    }                                                                                     
    > .active > a {                                                                       
      &,                                                                                  
      &:hover,                                                                            
      &:focus {                                                                           
        color: @navbar-custom-link-active-color;                                          
      }                                                                                   
    }                                                                                     
    > .disabled > a {                                                                     
      &,                                                                                  
      &:hover,                                                                            
      &:focus {                                                                           
        color: @navbar-default-link-disabled-color;                                       
        background-color: @navbar-default-link-disabled-bg;                               
      }                                                                                   
    }                                                                                     
  } 

```

Is there any detailed tutorial for less.js that I can refer?

Answer: 
Greater Than
------------

As Harry mentioned, the greater than `>` sytax is the same as in regular CSS, namely that the 2nd listed element is a child of the first element. 

See the table under `Selectors based on relationships` on [**this**](https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Getting_started/Selectors) URL:

`A > E: Any E element that is a child of an A element` 

Ampersand
---------

The ampersand is a shortcut to reference the current parent selector, so in your first example, the pure css would end up looking like this: 

```
  navbar-nav:hover,                                                                            
  navbar-nav:focus {                                                                           
    color: @navbar-custom-link-hover-color;                                           
  }    

```

[**Here**](http://thesassway.com/intermediate/referencing-parent-selectors-using-ampersand) is a good article explaining the use of the ampersand character in LESS/SASS

Tutorial
--------

While not exactly tutorial, here is the [**complete Language reference for LESS**](http://lesscss.org/features/#parent-selectors-feature) (linked to the section about referencing parent selectors with `&`)
`>` means the same thing that it does in regular CSS - it targets only direct children of the parent element.

`&` means that the selector is added onto the parent selector. For example:

LESS
----

```
.header {
  &:first-child {
    background-color: #fff;
  }
}

```

Pure CSS Equivalent
-------------------

```
.header:first-child {
  background-color: #fff;
}

```