“玄之又玄 众妙之门” concludes the first chapter of the Dao De Jing. In pinyin, “xuán zhī yòu xuán, zhòng miào zhī mén,” hence ZMZM.
Here’s my ambiguity- and pun-preserving translation of the Dao De Jing’s first chapter.
道可道 非常道 名可名 非常名
The apparent apparatus is no constant apparatus
The known noumenon is no constant noumenon
The meant meaning is no constant meaning
The named name is no constant name
無名天地之始 有名萬物之母
Without being named the beginning of heaven and earth
With being named the mother of ten thousand things
故常無欲 以觀其妙 常有欲 以觀其徵
Thus constantly without desiring to sight the marvelous
Constantly with desiring to sight the mundane
此兩者同出而異名 同謂之玄
These two being synonyms of the same source,
Together called mystery
玄之又玄 衆妙之門
Mystery, mystery recursing
The gateway to Wonderland