Changes

| reference || relative to which timepoint is the delay specified, either:  

| reference || relative to which timepoint is the delay specified, either:  

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| ^ || 'now': delay is specified relative to timepoint of bs_send_buffer_marker execution  

| || 'now': delay is specified relative to timepoint of bs_send_buffer_marker execution  

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|-

| ^ || 'marker' (default): delay is specified relative to the onset of the event during which bs_send_buffer_marker is executed  

| || 'marker' (default): delay is specified relative to the onset of the event during which bs_send_buffer_marker is executed  

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