lead position; first position (in a string)
Computing term for the initial position in a sequence, such as the first character in a string or the first element in a list.
Start the search from the first position of the string.
先頭 means 'head' or 'front' in a general sense, while 先頭位置 specifically refers to the position index in computing contexts.
Compound of 先頭 (head, front) and 位置 (position). A straightforward technical term.