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This represents cases where one or more single strands of hair are drawn out of place, separated from the bulk of the hair style. Sometimes, this is an element of messy hair or floating hair where a clean hairstyle is disrupted, but can also appear on the periphery of otherwise orderly hair, or in front of a character's face, as with many cases where a strand of hair is stuck to one's mouth, or ahead of the bulk of the hair as a distinct loose stroke.
Note that this tag is only for single strands of hair, these will be usually drawn in a single stroke, either in black, white, or a shade of the color of the hair. It is not for bundles, spikes, wedges, or clumps of hair. It is not for ahoge, antenna hair, cowlicks, sidelocks, or the like. For those, be sure to include the appropriate tag. If a bit of hair has a distinct border of another color, or a significant width or taper, it is almost certainly not applicable for this tag.
Although they might be drawn similarly, this is also not for stray pubic hair, or body hair.
Note that this phenomenon is often very hard or impossible to see in thumbnails, be cautious when gardening this tag.