Changing patio/balcony doors to sliders. Need a DOB permit?

We want to replace our existing balcony/patio doors. They meet conditions a,b, and c below, but we are seeking to change from casement style to slider. The rough amount of “operability” is the same, but what does “there is no change in the operable area of the window” mean. Does it mean “no change in the measurable area (the amount of square inches or feet) of the operable part?” or “no change in the type of operation (how it opens or closes)?” Per DOB, no permit necessary where: 1\. Replacement of existing windows (balcony doors) that satisfy the following conditions: a. such window is not located on the lot line; and b. the replacement does not require a modification of existing masonry openings; and c. the replacement window does not affect access to light or ventilation; and d. there is no change in the operable area of the window. Any help would greatly appreciated.