In this task, we ask you to rewrite a sentence in simple English without changing its general meaning. Essentially, you want to make the sentence easier to read by using simpler words, utilizing more straightforward sentence structures, and omitting non-essential information etc.

In humans , the pigmentation of the iris varies from light brown to black , depending on the concentration of melanin in the iris pigment epithelium ( located on the back of the iris ) , the melanin content within the iris stroma ( located at the front of the iris ) , and the cellular density of the stroma .
In humans , the pigment of the iris varies from light brown to black .

Among those who do refer to themselves as trans women , many see it as an important and appropriate distinction to include a space in the term , as in " trans woman " , thus using " trans " as merely an adjective describing a particular type of woman ; this is in contrast to the usage of " transwoman " as one word , implying a " third gender " .
Because of this many see it as important to include a space in the name , as in " trans woman " , using " trans " as a word to talk about a particular type of woman , not a " third gender " as " transwoman " might imply .

Engineers , as practitioners of engineering , are professionals who invent , design , analyze , build , and test machines , systems , structures and materials to fulfill objectives and requirements while considering the limitations imposed by practicality , regulation , safety , and cost .
Engineers design materials , structures , machines and systems while considering the limitations imposed by practicality , safety and cost .