When loading a shader with Raylib, a few properties are set automatically. The list of properties can be found in Raylib’s OpenGL library .
#define RL_DEFAULT_SHADER_ATTRIB_NAME_POSITION "vertexPosition" // Bound by default to shader location: RL_DEFAULT_SHADER_ATTRIB_LOCATION_POSITION
#define RL_DEFAULT_SHADER_ATTRIB_NAME_TEXCOORD "vertexTexCoord" // Bound by default to shader location: RL_DEFAULT_SHADER_ATTRIB_LOCATION_TEXCOORD
#define RL_DEFAULT_SHADER_ATTRIB_NAME_NORMAL "vertexNormal" // Bound by default to shader location: RL_DEFAULT_SHADER_ATTRIB_LOCATION_NORMAL
#define RL_DEFAULT_SHADER_ATTRIB_NAME_COLOR "vertexColor" // Bound by default to shader location: RL_DEFAULT_SHADER_ATTRIB_LOCATION_COLOR
#define RL_DEFAULT_SHADER_ATTRIB_NAME_TANGENT "vertexTangent" // Bound by default to shader location: RL_DEFAULT_SHADER_ATTRIB_LOCATION_TANGENT
#define RL_DEFAULT_SHADER_ATTRIB_NAME_TEXCOORD2 "vertexTexCoord2" // Bound by default to shader location: RL_DEFAULT_SHADER_ATTRIB_LOCATION_TEXCOORD2
#define RL_DEFAULT_SHADER_ATTRIB_NAME_BONEIDS "vertexBoneIds" // Bound by default to shader location: RL_DEFAULT_SHADER_ATTRIB_LOCATION_BONEIDS
#define RL_DEFAULT_SHADER_ATTRIB_NAME_BONEWEIGHTS "vertexBoneWeights" // Bound by default to shader location: RL_DEFAULT_SHADER_ATTRIB_LOCATION_BONEWEIGHTS
#define RL_DEFAULT_SHADER_UNIFORM_NAME_MVP "mvp" // model-view-projection matrix
#define RL_DEFAULT_SHADER_UNIFORM_NAME_VIEW "matView" // view matrix
#define RL_DEFAULT_SHADER_UNIFORM_NAME_PROJECTION "matProjection" // projection matrix
#define RL_DEFAULT_SHADER_UNIFORM_NAME_MODEL "matModel" // model matrix
#define RL_DEFAULT_SHADER_UNIFORM_NAME_NORMAL "matNormal" // normal matrix (transpose(inverse(matModelView)))
#define RL_DEFAULT_SHADER_UNIFORM_NAME_COLOR "colDiffuse" // color diffuse (base tint color, multiplied by texture color)
#define RL_DEFAULT_SHADER_UNIFORM_NAME_BONE_MATRICES "boneMatrices" // bone matrices
#define RL_DEFAULT_SHADER_SAMPLER2D_NAME_TEXTURE0 "texture0" // texture0 (texture slot active 0)
#define RL_DEFAULT_SHADER_SAMPLER2D_NAME_TEXTURE1 "texture1" // texture1 (texture slot active 1)
#define RL_DEFAULT_SHADER_SAMPLER2D_NAME_TEXTURE2 "texture2" // texture2 (texture slot active 2)