x1=tcit1=s3 is a tense (PU, etc.) of/based on/derived from x2=tcit3=tcin1 (e.g. «se cabna» ({se} used for tense (see CLL 10.23)) relative to x3 (default) (e.g. «mi» or the bridi) for sumti x4=tcit2=s1 of selbri x5=s2.
x3 is essentially the default tense object when it is zo'u'i, which CLL specifies is generally the speaker / ‘me’ (e.g. the x1 of «se purci» for «pu broda»), but can refer to the bridi (e.g. «mi pu'o broda»), perhaps creating a ‘higher bridi’ in relation to the ‘inner’ bridi of «mi broda», or alternatively modifying it to refer to the time interval before (the time interval that is «purci») «mi broda» (note, however, that «mi broda pu'o lonu brode» means that you broda until brode, so under this interpretation there is an assymetry (by x3) between «mi pu'o broda» ＝ «mi broda pu'oku» ＝ «mi broda pu'ozo'u'i», and «mi broda pu'o ko'a», which means ‘I broda until it’, like «mi broda pu'ozo'u'au». zo'e can be zo'u'i (default) as a hint, but zo'e can also represent an arbitrary sumti; zo'u'au is generally zo'e except non-default, so here «mi broda pu'ozo'u'au» means «mi broda pu'o ko'a» and such like.). Suggestion: given the traditional use of e.g. «caku», «caku» can be understood to mean «cazo'eku» that especially means «cazo'u'iku» given this context but technically can also mean «cazo'u'au» or «cako'a»; «cazo'u'iku» is a more explicit «caku», as is «ca[tu'a]mi». See also: zo'u'i (default sumti), zo'u'au (non-default sumti), pavtcinysumtcita (modal), tcinysumtcita (modal/tense).