Pandas dt.is_month_start: Checking period boundaries in a series

Want to know if values in a Python Pandas datetime series are at the start/end of a period? Get a boolean series from:

df['x'].dt.is_month_start     # or dt.is_month_end
df['x'].dt.is_quarter_start   # or dt.is_quarter_end
df['x'].dt.is_year_start      # or dt.is_year_end