@property<EOL><INDENT>def chrom(self):<DEDENT>
if self.item is None:<EOL><INDENT>return self._chrom<EOL><DEDENT>else:<EOL><INDENT>if self._chrom != self.item.chrom:<EOL><INDENT>raise IndexError("<STR_LIT>" +<EOL>"<STR_LIT>")<EOL><DEDENT>return self.item.chrom<EOL><DEDENT>
:return: the chromosome this block is one in the reference seq.