Ruby で、

str = "@time;prop1:style1;prop2:style2"

re = /((^|[@;])[^@;]*)/

p results = str.scan( re )
# [["", ""], [";prop1:style1", ";"], [";prop2:style2", ";"]]

[ 0 ]がマッチした部分、[ 1 ]がキャプチャー部分

>>862
の、["", ";prop1:style1", ";prop2:style2"] と同じ結果