docs: def checkformat(self):
          """************************************************************************************************************************************************************
          Task: checks the format of the bed file. The only requirements checked are that each line presents at least 3 tab separated columns, the
              two on the right must present integer values indicating the start/end position respectively. Right value must be greater than the
              left value.
          Outputs:
              err: string containing the detected error. Empty string in case of a correct format.
          ************************************************************************************************************************************************************"""
  
          fd = open_gzipsafe(self.filename)
  
          line = fd.readline()
          while line.startswith('#'):
              line = fd.readline()
          
          fields = line.split('\t')
          lc = 1
          error = ''
  
          # Checks that the two columns on the right contain integer values
          try:
              # Parses each line and checks that there are at least 3 fields, the two on the right containing integer values and being the right one
              # greater than the left one
              while line != '' and len(fields) > 2 and int(fields[1]) <= int(fields[2]):
                  lc += 1
                  line = fd.readline()
                  fields = line.split('\t')
          except ValueError:
              error += 'Incorrect start/end values at line ' + str(lc) + '\n'
              error += 'Start/End coordinates must be indicated with integer values. The right value must be greater than the left value.\n'
              error += 'Line found: ' + line
              fd.close()
  
              return error
  
          # If it get to this point means that either the file ended or there is a line with less than 3 fields
          if line != '':
              error += 'Incorrect line format at line ' + str(lc) + '\n'
              error += 'At least three columns are expected in each line\n'
              error += 'The right value must be greater than the left value.\n'
              error += 'Line found: ' + line
              fd.close()
  
          return error