Extracted from a document of glGetTexEnv (https://www.opengl.org/sdk/docs/man2/)
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GL_TEXTURE_ENV_MODE
params returns the single-valued texture environment mode, a symbolic constant. The initial value is GL_MODULATE.

GL_TEXTURE_ENV_COLOR
params returns four integer or floating-point values that are the texture environment color. Integer values, when requested, are linearly mapped from the internal floating-point representation such that 1.0 maps to the most positive representable integer, and 
-1.0
 maps to the most negative representable integer. The initial value is (0, 0, 0, 0).

GL_TEXTURE_LOD_BIAS
params returns a single floating-point value that is the texture level-of-detail bias. The initial value is 0.

GL_COMBINE_RGB
params returns a single symbolic constant value representing the current RGB combine mode. The initial value is GL_MODULATE.

GL_COMBINE_ALPHA
params returns a single symbolic constant value representing the current alpha combine mode. The initial value is GL_MODULATE.

GL_SRC0_RGB
params returns a single symbolic constant value representing the texture combiner zero's RGB source. The initial value is GL_TEXTURE.

GL_SRC1_RGB
params returns a single symbolic constant value representing the texture combiner one's RGB source. The initial value is GL_PREVIOUS.

GL_SRC2_RGB
params returns a single symbolic constant value representing the texture combiner two's RGB source. The initial value is GL_CONSTANT.

GL_SRC0_ALPHA
params returns a single symbolic constant value representing the texture combiner zero's alpha source. The initial value is GL_TEXTURE.

GL_SRC1_ALPHA
params returns a single symbolic constant value representing the texture combiner one's alpha source. The initial value is GL_PREVIOUS.

GL_SRC2_ALPHA
params returns a single symbolic constant value representing the texture combiner two's alpha source. The initial value is GL_CONSTANT.

GL_OPERAND0_RGB
params returns a single symbolic constant value representing the texture combiner zero's RGB operand. The initial value is GL_SRC_COLOR.

GL_OPERAND1_RGB
params returns a single symbolic constant value representing the texture combiner one's RGB operand. The initial value is GL_SRC_COLOR.

GL_OPERAND2_RGB
params returns a single symbolic constant value representing the texture combiner two's RGB operand. The initial value is GL_SRC_ALPHA.

GL_OPERAND0_ALPHA
params returns a single symbolic constant value representing the texture combiner zero's alpha operand. The initial value is GL_SRC_ALPHA.

GL_OPERAND1_ALPHA
params returns a single symbolic constant value representing the texture combiner one's alpha operand. The initial value is GL_SRC_ALPHA.

GL_OPERAND2_ALPHA
params returns a single symbolic constant value representing the texture combiner two's alpha operand. The initial value is GL_SRC_ALPHA.

GL_RGB_SCALE
params returns a single floating-point value representing the current RGB texture combiner scaling factor. The initial value is 1.0.

GL_ALPHA_SCALE
params returns a single floating-point value representing the current alpha texture combiner scaling factor. The initial value is 1.0.

GL_COORD_REPLACE
params returns a single boolean value representing the current point sprite texture coordinate replacement enable state. The initial value is GL_FALSE.
