HashTable .....

Hi C++ Experts,

     I am trying to understand a HashTable class template and its implementation. But there are several places I couldn't figure out why. I would appreciate some helps.

Here is the class template of a  HashTable :
(from Data Structure with C++, Schaum's)
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template <class K, class T, class H=Hash<K> >

class HashTable
{ protected :
    typedef pair<K,T> Pair ;
    typedef vector<Pair> Vector ;
    typedef Vector::iterator VIt ;
    typedef Vector::const_iterator CVIt ;
    static const float LOAD ; // line 01, Q1
    static const CAP = 109 ; // line 02, Q2

  public :
    HashTable(int cap=CAP, const H& h=H() ) : _(cap), _hash(h) {}
    T& operator[](K) ;
    bool insert(K,T) ;
    bool remove(K) ;
    int size() const ;
    int capacity() const { return _.size() ;}
    void dump const ;

  protected :
    Vector _ ;
    H _hash ;
    int hash(K) ;
    void rebuild() ;
} ;

template <class K, class T, class H>
const float HashTable<K,T,H>::LOAD = 0.75 ;  // line 03, Q1

template <class K, class T, class H>
T& HashTable<K,T,H>::operator[](K key)
{   const K ZERO_K = K() ;
    int k0 = hash(key), k = k0 ;
    while (_[k].first != key && _[k].first != ZERO_K)
      k = (k+1)% _.size() ;

    if( _[k].first == key) return _[k].second ;
    if( size()+1 < LOAD* _.size())        // line 04, Q1
    {  _[k] = Pair(key, T()) ;
       return _[k].second ;
    }
    else
    {  rebuild() ;
       return operator[](key) ;
    }
}

template <class K, class T, class H>
int HashTable<K,T,H>::size() const
{   int n = 0 ;
    const K ZERO_K = K() ;
    for(int i = 0 ; i<_.size(); i++)
      if (_[i].first != ZERO_K) ++n ;
    return n ;
}

template <class K>
struct Hash
{
   int operator()(K s)
   { int h = 0 ;
     for (int i = 0; i< s.length(); i++)
       h += s[i] ;
     return h ;
   }
} ;
blah ... blah ... blah ...
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Here are my questions :
Q1 : line 01, 03, 04 : I have trouble understand the variable LOAD. I don't really know why we need it and what does it do ?

Q2 : line 02 : I thought a static variable of a class can NOT be defined inside the class ? It has to be defined outside the class like LOAD in line 03. Or did I miss understand anything ?

Q3 : Is there a built in HashTable class Template in STL ? or there is only <map> in STL ??

Thanks !!!

meow.