def _format_lines(lines: Sequence[str]) -> list[str]:
    """Format the individual lines.

    This will replace the '{', '}' and '~' characters of our mini formatting
    language with the proper 'where ...', 'and ...' and ' + ...' text, taking
    care of indentation along the way.

    Return a list of formatted lines.
    """
    result = list(lines[:1])
    stack = [0]
    stackcnt = [0]
    for line in lines[1:]:
        if line.startswith("{"):
            if stackcnt[-1]:
                s = "and   "
            else:
                s = "where "
            stack.append(len(result))
            stackcnt[-1] += 1
            stackcnt.append(0)
            result.append(" +" + "  " * (len(stack) - 1) + s + line[1:])
        elif line.startswith("}"):
            stack.pop()
            stackcnt.pop()
            result[stack[-1]] += line[1:]
        else:
            assert line[0] in ["~", ">"]
            stack[-1] += 1
            indent = len(stack) if line.startswith("~") else len(stack) - 1
            result.append("  " * indent + line[1:])
    assert len(stack) == 1
    return result
Format the individual lines.

    This will replace the '{', '}' and '~' characters of our mini formatting
    language with the proper 'where ...', 'and ...' and ' + ...' text, taking
    care of indentation along the way.

    Return a list of formatted lines.
    
src/_pytest/assertion/util.py